I loved Sonic 6 for B&W Game Boy when I was little. I found out 7 years later it's a ROM hack.
http://www.youtube.com/watch?v=cIaBLabKZMA
Still, Pokemon is the best by a long shot.

Kid Icarus 2.

I enjoyed Donkey Kong Land III, it was my first Game Boy game. I also liked Pokemon Gold and Shantae.

guys the best game i had played in this game boy was with a helicopter (i can't remember the name of the game).
you had the helicopter and you had to rescue people from the earth using rope and other methods depending the situation...
Anyone have played or remember the name of that game??
super mario 2, castlevania and xmen were also very good games...

Donkey Kong. it begins with the original arcade game, then develops into a fantastic puzzle-platformer.

I'd say Pokemon Yellow Version.

Pokemon Crystal
Pokemon Gold
Pokemon Silver
Pokemon Yellow
Pokemon Blue
Pokemon Red

Simple as that.

Another top five GB tread, but what the heck, here's my top five GB (not GBC) games:

1. Tetris
2. Pokémon Red, Blue & Yellow
3. The Legend of Zelda: Link's Awakening
4. Wario Land: Super Mario Land 3
5. Super Mario Land 2: Six Golden Coins

LINK'S AWAKENING!!!
Well, the DX version anyway.

Ah yes, that game doesn't get nearly as much respect as it deserves.

Pokemon

Link's Awakening!!

DONKEY KONG

Kirby's Dreamland 2 and Wario Land I and II. None of the rest come close.

1. Tetris
2. Super Mario Land (1) (easy game but great fun to play through)
3. Mario Picross
4. Golf
5. Qix

Pokemon and Lil' Monster

just had to throw a shout-out to toki tori and balloon kid.

Final Fantasy Adventure is pretty good too, despite its flaws in dialogue.

My favorite Gameboy game is my 82 in 1 multicart

But my favorite standalone game is Darkman. Very cool fighter/brawler. I love it.