Heres a selection of Homebrew from the GBA:

100 Boxes puzzle
5nake
Advance Debugger 0.36
AGB Midi
Akop
Anguna
Bauble Break
Beerbong
Billy Box
BricksOS
Broken ASCII Digger
Broken Circle
CCCP
Chessyka
Chocobo World Deluxe
Christmas Pong
Cleangame Advance
Clem the Retarded Elf
Clonker Advance
Codename Hacker GBA
Defi De Noel 2007
Droplets
El Tío sin Chorra
Factory Bots
GBA Exploader
GBA Notepad
GBA program that enters GBC mode.
Gearhead Garage Adventure
Goldeneye Advance
Gorf
Gravity Ball Advance
Hexavirus
Hively Player Advance
Holy Hell
Impact
Jumping Barnabe
Lockjaw
Mammary Advance
M-Dezign
MMNH
Motocross Challenge
Negative Space
Nicky Boum
Niilon Tarina GBA
Numchuck and the Conquest of Color
OpenPoke
Paper Scissor Rocks GBA
Pixelh8 Music Tech Pro Performer
Pocket Commander
Pocket Raider
Pocket Raider 2
Poomania
Powder - Rogue Clone
Prison Break
Racer
Reaxion
ReBoy
Return to Genesis
S3MMix5
S3M Plus
Season Stacker
Shapes GBA
Snake
Sonic AS
Sonic GBA
Starcraft Ghost
Storm
SUPER MARIO : The Last GBA Quest
Super Wings
SynthGBA
Tailgunner GBA
The Snowman
Time Walker
Trogdor The Burninator
Turok Advance
Unibrau
Vero Design Advance
Vincent GBA
Vortex Generator
World Reborn
Yet Another SFCave
Znax