In a LD deck it's important to balance your spells out. For example, you will more than likely want at least 20 LD spells. Because most decks play with at least 20 land in them. Now, let's look at some different decent LD cards for certain colors:

RED:

• Stone Rain: your average LD spell for 2R. The one red in the casting cost makes it easier to cast early in the game. If you have a LD deck with red in it then you need these in there.
• Pillage: Land Destruction and Artifact Destruction for 1RR. The double red mana needed to cast the spell can be a problem sometimes, but this card is needed to get rid of pesky artifacts as well as land.
• Raze: R for LD? Sounds good. Only problem is you have to sac a land when you cast it. This could be a problem, or it might not even matter. You can look at it this way, it lets you turn one of your lands into a strip mine so to speak. However, you lose a card in your hand. I've found it works wonders against speed decks or against another LD deck for that matter.
• Avalanche Riders: 3R for a 2/2 with haste and you destroy a land when they come into play. They have echo, but big deal. Get rid of a land and hit em for 2. If they don't play a land their turn go ahead and pay the echo so you have a creature out. It's a great card.
• Wildfire: okay. This can be very useful. 4RR and everyone sacs 4 lands and then 4 damage to all creatures. It shouldn't bother your creatures much because they should be big enough to handle 4 damage. And saccing 4 lands shouldn't bother you either because you should have more lands than your opponent anyway.
• Orcish Settlers: these can be fairly useful. 1R for a 1/1. Pay XXR TAP and sac and destroy X target lands. Of course, if your deck is working, why would you need these? There are other red LD cards that I could mention, but they don't really impress me very much when it comes to good LD cards. There is flowstone flood, but do you really want to pay 3 life and discard a card to buy the spell back? Anyway, on to other colors.

GREEN:

• Ice Storm: As with Stone Rain this card is your basic LD for 3, and the 2G casting cost is easy to pull off early in the game. These are needed for a LD deck with green in them.
• Creeping Mold: this is just a nice card. 2GG for Land Destruction, Artifact Destruction, OR Enchantment Destruction. Now if only it could kill creatures, but oh well. The 2 green mana needed could hold you up from using it, but if you have duals etc it shouldn't be too big of a problem.
• Thermokarst: well, LD for 1GG. Not that bad, and if it's snow-covered (for all those IA lovers) you gain 1 life. Not too bad, but not as good as the others.
• Winter's Grasp: LD for 1GG. That's it. If you are going to use these, just use the Thermokarst. They might be using some snow-covered.
• Desert Twister: well....4GG to destroy any permanent on the board isn't all that bad. Can be useful for when your opponent has out an annoying enchantment, artifact, land, or creature.

BLACK:

• Sinkhole: the best black LD card. BB to destroy any land. Pretty nice, definately a must for LD decks with black in them. The 2 black mana needed can slow you down possibly, but it shouldn't be too bad.
• Icequake: Like it's green counterpart, Icquake is 1BB to destroy a land. And if the land is snow-covered then icequake deals 1 damage to them. It isn't all that bad.
• Choking Sands: 1BB to destroy a land. Not bad, but you can't destroy swamps with it, however if you destroy a non-basic land with it, then the land's controller loses 2 life. Which can be good. Can be put in the sideboard possibly.
• Rain of Tears: well....1BB to destroy a land. And that's it. Go with Icequake.
• Befoul: now this is a good card. 2BB to destroy either a non-black creature or a land. Can be very useful for creature elimination. I'd suggest putting 4 in the deck. Okay, now that we have looked at the LD spells, let's take a look at the other types of spells needed in a LD deck.

FAST MANA:
You need fast mana in a LD deck. You have to be able to produce mana very quickly so you can start blowing up land as soon as possible. Now I'll list the different choices for fast mana.

• Birds of Paradise: G for a 0/1 flier that can be tapped for any color mana you want? These are great for any LD deck involving green and another color.
• Tinder Wall: G for a 0/3 wall that can be sacced for RR. If you pay R and sac it, then it deals 2 damage to a creature it blocks, which can be useful. The fast red mana is also useful for when you need 2 red mana for one spell early in the game.
• Dark Ritual: this is just a must for any LD deck with black in it. All you need is one swamp out and you can destroy a land if you have a ritual.
• Orcish Lumberjack: okay a 1/1 for R. Sac a forest and add 3 mana of any combination of red and green to your mana pool. This can help too if you don't mind losing the forest.
• Sol Ring: this is just great. With one of these out you can cast a stone rain, ice storm, etc on your second turn. Definately a must.
• Agent of Stromgald: I know that at first this seems pointless. But a 1/1 for R that can turn red mana into black mana can be great if you are running low on black mana, but all you have is red.
• Various Mana Elves: these are just the basic mana producing elves such as Llanowar Elves, Fyndhorn Elves, Quirion Elves. They help.
• Moxen and Lotus: if you have these, use them. Enough said.

CREATURES
Creatures are important in an LD deck because you need a way to defeat your opponent. And if the have no land out, then it makes it harder for them to kill the creatures or summon creatures to block them.

• Argothian Wurm: 6/6 Trample for 3G. What's the downside? Anyone can sac a land when it comes out to put it on top of it's owner's library. Well, this can work for you rather than against you. Let's say they have no land out? Well, darn, guess they can't put it on top of the library then huh? Or let's say they do have land out. You make them choose. Lose a land or deal with a 6/6 trample. Of course, even if they do sac the land they will have to deal with the wurm again the next turn, making them choose once again.
• Lava Runner: I know it's only a 2/2, but it has haste and if someone targets it they have to sac a land. And it only costs 1RR, so it isn't that bad really.
• Balduvian Horde: 5/5 for 2RR and you have to discard a card when they come into play. Oh well, it's a 5/5 creature for 4. It's great.
• Demonic Hordes: 3BBB for a 5/5 and you have to pay BBB during your upkeep or they tap and you lose a land of your opponents choice? But look at the good part. If you tap them, you get to destroy a land. It's a nice creature.
• Erhnam Djinn: 4/5 for 3G. During your upkeep you have to give one of your opponent's creatures forestwalk. Well, with no mana...they can't cast creatures...so I guess you don't have to worry about forestwalk do you?
• Juzam Djinn: 5/5 for 2BB. It deals 1 damage to you during your upkeep. Darn, the thing is awesome. Can't be terrored etc. and it's a 5/5 which is nice. So what if you lose 1 life each turn, you'll more than likely be dealing 5 or more to them.
• Shivan Dragon: gotta love 5/5 flying creatures. Of course it costs 4RR, but it can be pumped up +1/+0 for R. It can be great for killing your opponent quickly.
• Kird Ape: okay a 1/1 for R, but if you control a forest it becomes a 2/3. Not bad in a R/G deck.
  

Of course there are other creatures you could use, but these are the ones that really got my attention for when I began making this.

VARIOUS SPELLS:
Sometimes, you just need some special types of spells to make your job easier.

• Regrowth: 1G to put any card from your graveyard to your hand is always helpful.
• Fork: RR and it copies the last cast sorcery, instant, or interrupt spell. Hey, destroy 2 lands, cast 2 bolts, or hell, copy their counterspell and counter their own counter. Can also fork a regrowth and get 2 cards etc. Lots of uses for this.
• Demonic Tutor: can help for when you need a certain card, but just aren't getting it. 1B to put any card from your library into your hand can be VERY useful.
• Stormbind: 1RG for an enchantment that lets you pay 2 and discard a card to deal 2 damage to any target. Good for removal and for killing your opponent faster.
• Well of Knowledge: 3 for an artifact that lets players draw extra cards during their draw phase at the cost of 2 per card. Well, if you have mana and they don't then you deserve some extra cards.
• Wheel of Fortune: not exactly my favorite card to use in LD, but it can help. 2R and everyone discards their hand and draws 7 new cards. Good for refilling your hand, but it could help them too.
• Tainted Aether: 2BB for an enchantment that says when anyone puts a creature into play they must either sac a land or another creature. Gotta love that, and you won't be casting too many creatures so it shouldn't hurt you much.
• Aether Flash: 2RR for an enchantment that deals 2 damage to any creature when it comes into play can shut down a creature deck. Especially when you get out multiple ones, but be careful, it could kill your own creatures.
• Lightning Bolt: R for 3 damage to any target. Gotta love it.
• Storm Seeker: 3G and it deals 1 damage to target player for each card in their hand. If they have no mana, then they won't be casting much, so they should have a full hand.
• Chain Lightning: another 3 damage for R. But it's not an instant and it could backfire if you're playing against another red deck.
• Cursed Scroll: hey, these could always help you deal some more damage. I prefer stormbind myself, but whatever you want to use.
• Fastbond: G for an enchantment that lets you play as much land per turn you want at the cost of 1 life per extra land played. This only really helps in the beginning of the game.
• Terror: 1B to destroy a nonartifact nonblack creature. This can help you if they get out pesky creayures.
• Diabolic Edict: 1B and your opponent chooses and sacs a creature. If they only have one out it can be great. It also gets around untargetable creatures and it can get rid of artifact and black creatures unlike most other black creature destruction.
• Dingus Egg: I know, I know. Why use this? My friend does and it helps him every now and then. It deals 2 damage to a player whenever one of their lands goes into the graveyard and you'll be blowing up a good amount of land right?
• Incinerate: 1R to deal 3 damage to any target, and if it's a creature it can't be regenerated which can come in handy.
• X damage spells: hell, if you have lots of mana, use it to kill them!

There are a lot more spells I could throw in here, but I feel these are some of the best ones for an LD deck. You can always add some more and let me know if I overlooked any. I'm sure I have. And last, but certainly not least. The lands:

• Duals: USE THESE!!!!!!!!
• Strip Mine: uncounterable LD. what can I say? Too bad they restricted these.
• Wasteland: uncounterable non-basic LD.
• Dust Bowl: turn any of your lands into a wasteland basically. pay 3 and sac a land to destroy a non-basic land.
• Rishadan Port: pay 1 and tap the port to tap a land. why let them use the land that they actually have anyway?
• Reflecting Pool: can act as a dual when it comes out at the right time, or it could just stick you with more of the same color you already had.