That's right, a Game Boy.

Not Game Boy Advanced, Color, Light, or anything fancy like a that, but a slab of solid grey plastic straight from 1989. My girlfriend got it from her grandmother, and gave it to me as a birthday gift. The only games she still had to give me were Pokemon Red, and some combi-cart with Tetris and some tank game. They're fun and everything, but some variety would be nice.

Therefore I'm asking you guys, what games on the old classic Game Boy due you recommend to me? I'm thinking of getting Kirby's Dream Land, but other than that my hand held knowledge is slim.

Damn it's been a while. Outside of Tetris, which is the undisputed greatest Game Boy game ever, I would say pick up Super Mario Land 2: 6 Golden Coins. It's mechanics are like SMW but the levels are all very unique, and the final boss is someone making their first appearance who went on to become big in his own right.

Pick up Castlevania Adventure and Castlevania II. It has annoying early Castlevania mechanics but is really a good game overall. 

Rubang will throw a conniption fit if someone doesn't mention the Legend of Zelda: Links Awakening, so get that too. You can pick up Mario's Picross, but it would probably be cheaper and better to just pick up Picross DS if you have a DS.

I'm pretty sure the Mega Man games were good on the Gameboy.

Final Fantasy Adventure was supposed to be pretty decent.

Outside of those, I'm spent. I used most of my Gameboy time on just Tetris, Castlevania Adventure and Super Mario Land 2. 

You HAVE to get Zelda: Links Awakening. It's one of the BEST Zelda games ever made. It's a must have! Go get it right now! ;)

I also highly recommend Final Fantasy Adventure and strongly suggest you avoid Final Fantasy Legend games (the leveling up is sooooooo slow in those games).

Kirby's Dreamland is another great game....

And of course you have to get Metroid II.  That was another awesome game.  I know it gets picked on a lot but it's still a lot of fun to play.

Here you go...

http://www.gamespot.com/features/vgs/universal/gameboy50/

Links Awakening is a must!

Kid Icarus is really nice!

Solar Striker is a nice simple oldschool shootemup

and I almost forgot

Metroid II, a really nice game that I have very fond memories of 

The Mega Man games are all pretty nic, but also damn hard

Super Mario Land 1 and 2, nice platforming

Besides the link I sent, here are my personal faves that still hold up...

Tetris
Dr. Mario
Donkey Kong (includes 100 boards & the complete original game)
Super Mario Land 2: 6 Golden Coins
Super Mario Land
Metroid II (Best portable metroid until Metroid Fusion.)
Kirby's Dreamland
Kirby's Dreamland 2
Kid Icarus
Donkey Kong Land 2
Donkey Kong Land
Donkey Kong Land III
Mega Man IV
The Legend of Zelda: Link's Awakening
Wario Land: Super Mario Land 3
Warioland II
Bomberman
Pokemon - Blue/Red
Final Fantasy Adventure

Kirby Pinabll!

Oh, and if you are REALLY up to a challenge, pick up Contra: Operation C. I believe it is the first portable Contra games, and is hard in that great Contra & Battle Toads way. Not too different from todays amazing Contra 4 for the DS.

The Bugs Bunny Crazy Castle is awsome! I really loved that game!
Mortal Kombat too :O
Super Mario Land... etc etc

Well everyone has mentioned the obvious, so I'll list some off beat games.

Mole mania
Alleyway
Navy blue
Castlian
Qix