I just brought the grey brick back into my collection but I've lost all my games.  I had Street Fighter and Zelda: Link's Awakening I recall.  I'm sure the Poke's were in there too. I'm planning on picking a few new used games up from a local place and I need some suggestions.  On the list are:
 

• Metroid 2
• Final Fantasy Adventure
• Super Mario Land 2
• Wario Land

Well, you already chose Metroid 2 and Mario Land 2.
You should get Link's Awakening back, though. That game is good. I can't remember any of the other games I used to play on the good 'ol brick.

I had Tetris and Battletoads which were both hard as fuck, but then I bought Pokemon and my life was complete.

The Game Boy version of Bionic Commando was pretty sweet.  I'd also recommend tracking down Final Fantasy Legend III.

I was thinking about Battletoads but didn't know if it was worth picking up.   I will have to get Link's Awakening back.  What about the Mega Man series?  Anything good there on Gameboy?

Gargoyles Quest was an awesome game, The only Final Fantasy that I actually played and passed was on the OG GB. Castlevania Adventure was great but never beat

I owned Legend 1 and 2 they...worked for the time period they were in.  Does Legend 3 make any improvements from 1 and 2?  Like removing decaying spells and weapons? Can I still "Eat the Meat" Hahahah

Balloon Kid is a very overlooked game you should get, as is The Final Fantasy Legend if you want an easy grindfest.

I will have to try to find Gargoyles Quest and Balloon Kid.  Possibly Bionic Commando too.  No more Legend 1 or 2 though.  I can't do that to myself any more.

How about the Gameboy version of Metal Gear Solid?

Wario Land was the shit! I use to love that game so much back in the day! I miss it! >_<

Hahaha it's only a small part of me trying to bulk up my collection.  Thanks for the advice Famov.  I'll be sure to check the carts before buying. I suppose I'll grab the poke's just to have them not to play.  I can't do that to myself again.  Ohhhh the scars from playing the same game twinges at the thought.   I haven't heard of Rolan's Curse.  I'll look it up.

Totally forgot about  Legend of Zelda: Link's Awakening! Played this game so much when it came out

I'm pretty certain that Metal Gear Solid was for Gameboy color Karmum.  I'm just looking for OG Gameboy games.
 
I, unfortunately, never have played Wario Land.  I've heard great things from the Retronauts.  I'm sold.  You guys have cemented the fact I need to get Wario Land 1 and 2.
 
Link's Awakening is amazing. Definitely a top Zelda game for anyone who knows the series. At risk of starting some stuff, I'll say it's my second favorite.

Mega Man IV and V are excellent games, though very pricey. My personal favorite GB game is Final Fantasy Adventure, much better than its GBA remake. Castlevania II: Belmont's Revenge is fairly decent too (the first is abysmal, watch out), and has excellent music.
 
Almost all of Nintendo's games for the system are still worth playing. Besides everyone else's suggestions, check out Mole Mania, it's a fun little puzzler released late in the system's life and forgotten.

Double Dragon, yo!! lol
 
The best ones have already been mentioned, so I'll just put in my vote for Wario Land 1 & 2 as well.
 
A few faves of mine when I was but a wee geekling were Metroid II, Kirby's Pinball Land and Pokemon Red. 
Oh, God, and Road Rash.

Thanks Eirikr.  Mole Mania looks interesting. If I can find it I'll grab it. I'll keep an eye out for cheap Mega Mans too.
 
I never was really into Kirby but he's got a few notable games on the brick right?  Anybody know a little more about those?

I had no idea Road Rash was on Gameboy.  I forgot about Double Dragon.  So many games.  Good thing they're no more than ten dollars a piece

Kirby's dreamland.
@Karmum said:

" How about the Gameboy version of Metal Gear Solid? "

" Kirby's dreamland.
@Karmum said:

" How about the Gameboy version of Metal Gear Solid? "

im pretty sure that was game boy color. "

I like easy.  Especially on a hand-held.  I'll grab Dreamland for sure.

Alright, I think that's enough to go on now.  Thanks for all the Game Boy recommendations.  I'll need help again when I pick up a neo geo pocket and a nomad.

Your list are some of the best games out there for it. I also enjoyed the first Castlevania game on there, and motorcross maniacs. I believe there was a ninja turtles game I loved as well. Not sure if they stand the test of time but I know back then they were cherished by me.