Recently I've been playing the hell out of some of my handhelds and the GameBoy has gotten most of the attention. Can anyone else recommend any other games to me? I currently have:

Adventure Island
Adventure Island II: Aliens in Paradise (this was pretty good)
Battle Arena Toshinden (yeah... I kind of have a soft spot for this severely outclassed series)
Castlevania: The Adventure
Castlevania II: Belmont's Revenge
Castlevania Legends
Crystalis (yeah, I've heard this isn't a good port)
Double Dragon 3: The Arcade Game
Donkey Kong Country
Donkey Kong Land
Donkey Kong Land 2
Donkey Kong Land III
Dr. Mario
DuckTales (the good old standby)
Kirby's Dream Land (not as good as I think; blame nostalgia)
Kirby's Dream Land 2
Mega Man
Mega Man II
Mega Man III
Mega Man IV
Mega Man V
Mega Man Xtreme
Mega Man Xtreme 2
Metroid II: Return of Samus (love this one)
Ninja Gaiden Shadow
Operation C
Pokemon Blue
Pokemon Red
Pokemon Yellow
Ren & Stimpy: Veediots! (admittedly terrible but I grew up with it)
Ren & Stimpy Show: Space Cadet Adventures (got it to see if it's as bad as Veediots)
Super Mario Bros. Deluxe
Super Mario Land
Super Mario Land 2: Six Golden Coins
TaleSpin
Tetris (cause you got to have Tetris if you have a GameBoy)
Tetris 2
The Legend of Zelda: Oracle of Ages
The Legend of Zelda: Oracle of Seasons
Tom and Jerry: Frantic Antics
Wario Land: Super Mario Land 3
Yoshi

Feel free to include Game Boy Color games (some of the games above are GBC games) but don't recommend Shantae... I don't have that kind of coin

Legend of Zelda:  Link's Awakening was always one of my favorite GameBoy games.

Perhaps I should have added a list of what I'm looking to nab... cause this is definitely on it. But then there is the fact there is two different versions: normal and DX.

Donkey Kong is one of the best, I highly recommend that. Shantae and Mole Mania are also great. If you like puzzle games, Mario's Picross entertained me.

Check out the Rolan's Curse games. Pretty unappreciated and rather Zeldaish.

I vaguely remember hearing that one of the GB Tomb Raider games was pretty good... does that ring a bell for anyone? I do like TR despite the fact some of the console games aren't my thing.

I've seen the Donkey Kong cart before but I unfortunately didn't pick it up. However, I've played Land I and III. Land III is really good but Land I can be kind of unforgiving. I picked Land 2 off the net tonight to complete my set... the Land series is dirt cheap and the games offer a lot.

I can't really justify this one considering the price... hell, the only reason I could justify buying a complete Misadventures of Tron Bonne last year was the fact I was giving my disc-only copy to my friend as a Christmas gift. I don't really want to spend that much on a game again...

...but I might end up spending a big amount of money on Dracula X if I get the remaining CV titles I need first.

Donkey Kong is completed unrelated to the Donkey Kong Land series; the former is a dramatic expansion of the original arcade gameplay, while the latter is portable Donkey Kong Country. I'm not saying one is better than the other, just markedly different. I enjoy Donkey Kong because it can be as much a puzzle as it is a platformer; rather than going from Point A to Point B, you have to figure out how to get from Point A to Point B.

Oh, as for Link's Awakening, I can't think of any reason compelling enough to choose the original over DX. Aside from the additional content, the differences between the two are minor/beneficial or negligible.

Oh, and if pinball's up your alley, Pokemon Pinball was highly addictive. I still pop in the GBA edition from time to time.

There are so many fun GB games but, after all these years, it is just the Zelda games and Pokemon Pinball which still get some real play. Pokemon Pinball is tons of fun and it's quite challenging - I still haven't completed the Pokedex (completed the GBA Pinball Pokedex just this year!).

I played through Link's Awakening again a few months back and it's easily my favourite Zelda game. I'm currently playing Oracle of Seasons and it's also really good.

Edit: You have Pokemon R/B/Y but not S/G/C. I guess the thing with Red, Blue, and the S/G/C series is that they all got remade and I would have a hard time seeing why the original versions would be better, although really Pokemon peaked for me with S/G/C - after that, catching 'em all kind of stopped being a reality and the appeal began to fade for me. But out of all of those, Yellow is still unique in terms of its content so it's definitely one to focus on there if you're going to go for a GB Pokemon game.

Another vote for Link's Awakening. Best game in the series, in my opinion.

Kirby's non-platformer games were much better and worth a look if you like puzzle games: Pinball, Blockball, Stacker

I know you're a fan of SaGa Frontier, so maybe you'd be interested in SaGa's roots in the Final Fantasy Legend Trilogy (rebranded SaGa games for the West). They're really good, especially SaGa2, if you can overlook the awful localization. Seiken Densetsu 1 aka Final Fantasy Adventure if you like your Zelda with leveling

Just chiming in. Awesome game, awesome music. I'd love to make my way through this one again at some point.

I'll second Link's Awakening, Final Fantasy Adventure, Donkey Kong and Final Fantasy Legend II.  I'll also add Gargoyle's Quest; if you like Capcom you must own it (even though it is the weakest in the trilogy it's still the original).

Is this related to Demon's Crest...?

Yeah, that's the third game (second was on the NES).

You have a very good selection already, but your collection would be even better if you added:

-Bionic Commando (the regular GB one, not Elite Forces for GBC)
-Donkey Kong 1994 (takes the gameplay of the original Donkey Kong and expands it greatly; this became the foundation of the Mario Vs. Donkey Kong games before they added the minis)
-Final Fantasy Adventure (aka Seiken Densetsu, best GB game ever, IMO!)
-Gargoyle's Quest (my favorite of the three in the series)
-Legend of Zelda: Link's Awakening DX (best handheld Zelda there is)
-Metal Gear Solid (also known as Ghost Babel)
-Shantae (just get this on 3DS Virtual Console, it's only around $5 on that)

Actually I was thinking about this one as well.

Also, despite the fact the original versions got slammed I thought I heard that Daikatana on the GBC was pretty decent.

Edit:

I've actually played a bit of this in the past and I would nab it if I'd come across it... yet it's funny you mention it because I happened to stumble upon the remake earlier today and I nabbed it since I had been looking for it.