I 100%ed one playthrough of Aria of Sorrow already, and I just finished Metroid Fusion. The games I am going to play next are:
 
Castlevania: Circle of the Moon  
Metroid: Zero Mission 
Castlevania: Harmony of Dissonance 
The Legend of Zelda: The Minish Cap  
 
Currently playing Circle of the Moon. It's really different than the other 3 Castlevania games I've played and loved (SOTN, AOS, POR) but I'm liking it nonetheless. I'm trying to switch the games up, so it'll be like Castlevania, then Metroid, Castlevania, Metroid, Castlevania, Zelda. I freaking LOVED Aria of Sorrow. Too bad I can't find Dawn of Sorrow anywhere for my DS :(
 
After I finish these games however I am going to need more because I'm becoming addicted! Please tell me of the best games on the system. No Pokemon though, I'm actually playing Diamond right now too on my DS and that is giving me my Pokemon fill. Thanks.  

Zero Mission is AWESOME, but I have just one thing to say: 
 
GOLDEN 
 
FUCKING 
 
SUN 
 
 
Golden Sun, my most favoritest GBA titles of all. 
 
Love, 
 UnlivedPhalanx

Golden Sun, Golden Sun The Lost Age, and Mario and Luigi Superstar Saga.

i've spent sooooo much time with Jurrasic Park III: Park Builder its insane

Final Fantasy Tactics advance is great :)

Old school Advance Wars and the Final Fantasy VI port are pretty good too

Final Fantasy Tactics Advance definitely, as well as The Legend of Zelda : A Link to the Past .

" Final Fantasy Tactics Advance definitely, as well as The Legend of Zelda : A Link to the Past . "

Warioland 4 is a cool platformer.

I can't recommend Fire Emblem (7) highly enough. It was the first game in the series released in english so you don't need to worry about it being overly difficult and it has the best plot out of any Fire Emblem game I've played.

Definitely check out the Sonic Advance trilogy or the Super Mario Advance remake series, particularly the ones  of Super Mario Bros. 3 and Super Mario World (Super Mario Bros. 4) if you're into classic platformers. The Sonic games have a really nice retro-yet-updated feel and the Mario remakes do a spectacular job polishing and updating some legendary games.
 
For RPGs if you like Final Fantasy there are the really solid remakes of I, II, IV, V and VI. The ones of IV and VI in particular are of exceptionally stellar quality-One of the things the GBA was really excellent at was updating and re-introducing classic NES and Super Nintendo games. Other than that, the Golden Sun games are probably the ones that stick out for me the most as well for RPGs.
 
One of the most memorable games on the Game Boy Advance for me was Advance Wars: It's a maddeningly delightful and addictive turn-based strategy game with a charming art style, a great sense of humour and really deep gameplay. The sequel, Advance Wars 2: Black Hole Rising, is also very good but the original is still my favourite. If you have a DS, there was a final entry in the story with Advance Wars Dual Strike and a retcon/reboot with Advance Wars Days of Ruin. The original GBA game is still the place to go for many fans though.

You should take a look at Sword of Mana and Astroboy: Omega Factor.  The first is a great JRPG although I think it is a remake from an earlier game.  The second is a great but under appreciated side-scrolling shooter.   This one took me a few years to find but I finally did and it is still great.  Balls to the walls fun with giant colorful explosions and effects. 

• Sword of Mana video
• Astroboy video

Fire emblems, FF 6, Boktai , Metroids( fusion and zero mission), Megaman zero 4...and so many others

Metroid Fusion
Zelda: Minish Cap
Warioware

Megaman Zero series

Metroid Fusion.

Dude... Mario & Luigi: Superstar Saga

Megaman Battle Network is a fun RPG series that ate up my time back in the GBA days. The first 3 are great, with 2 or 3 usually being considered the best.

" Dude... Mario & Luigi: Superstar Saga "

" Warioland 4 is a cool platformer. "

Golden Sun for sure!

Sweet guys, now I have so much to look forward to! Definitely going to check all of these out. I'm especially excited for Golden Sun now :D

• The Legend of Zelda: The Minish Cap - My second favorite Zelda game, right after A Link to the Past.
• Mega Man Battle Network 3 (and, if you like it, the others) - One of my favorite role-playing games.
• Dragon Ball Z: The Legacy of Goku 2 - A great beat 'em up with light RPG elements.
• Pokemon Sapphire - My personal favorite Pokemon game.
• Mega Man Zero 1-4 - Superb side-scrollers.
• Summon Night: Swordcraft Story 2 - A fun little JRPG.

1. Castlevania: Aria of Sorrow  
2. Mario & Luigi
3. Metroid Fusion
4. Golden Sun
5. Advance Wars 2
   
6. Wario Ware, Inc
7. Kirby: Nightmare in Dream Land
8. Yoshi's Island Super Mario Advance 3
   
9. Super Mario Bros. 3
10. Pokemon Pinball
    
11. Zelda: A Link to the Past
12. Snood
    

Hmmm admitting you are using an emulator? not very smart, shouldn't this be locked?

Personal Gameboy Collection

Of all Gameboy consoles, these are the games I own

	1. Golden Sun: The Lost Age finished (twice)
	2. Pokémon Gold/Silver finished (twice)
	3. Shantae finished
	4. Castlevania: Circle of the Moon nearly finished
	5. Final Fantasy VI
	6. Golden Sun finished (twice)
	7. Fire Emblem finished
	8. Castlevania: Aria of Sorrow finished
	10. The Legend of Zelda: A Link to the Past played
	11. Advance Wars nearly finished
	12. Yggdra Union: We'll Never Fight Alone played
	16. Metroid: Zero Mission finished
	17. Zone of the Enders: The Fist of Mars finished (twice)
	18. Riviera: The Promised Land finished
	19. Tales of Phantasia played
	20. Super Street Fighter II: Turbo Revival played
	23. Mario Kart: Super Circuit finished
	25. Gunstar Super Heroes
	26. Fire Emblem: The Sacred Stones finished
	27. Final Fantasy V
	28. Final Fantasy I & II: Dawn of Souls finished
	29. Drill Dozer played
	30. Astro Boy: Omega Factor
	31. Boktai 2: Solar Boy Django
	32. Boktai: The Sun is in Your Hand

Definitly Golden Sun 1+2

Astro Boy: Omega Factor. One of the Top 5 best action games on the GBA.

" I can't recommend Fire Emblem (7) highly enough. It was the first game in the series released in english so you don't need to worry about it being overly difficult and it has the best plot out of any Fire Emblem game I've played. "

"Zero Mission is AWESOME, but I have just one thing to say:  GOLDEN  FUCKING  SUN   Golden Sun, my most favoritest GBA titles of all.  Love,  UnlivedPhalanx "

" Dude... Mario & Luigi: Superstar Saga "

Fire Emblem (both), Advance Wars (both) & Final Fantasy Tactics Advance are by far, the best games on the GBA.

How about you, like, don't pirate shit?

" How about you, like, don't pirate shit? "

Golden Sun
Golden Sun 2: The Lost Age
Final Fantasy Tactics Advance
Metroid Fusion
The Legend of Zelda: A link to the Past

I used to love the Mega Man Battle Network franchise. At least the first few.

warioware: Twisted.

megaman, megaman battle network, fire emblem, pokemon, final fantasy remakes, mario world,  zelda, superstar sega, and a whole lot more

" Warioland 4 is a cool platformer. "

My Top 11 GBA list
 http://www.giantbomb.com/profile/captainlunchbox/top-10-plus-1-gba-games/46-39721/ 

River City Ransom.

Shining Soul 2.  Great Diablo clone!

I believe Tetris Worlds was on the GBA? Should be dirt cheap now, check it out.