Well technically June 11th. The following games were released at launch:

Army Men Advance
Castlevania: Circle of the Moon
Chu Chu Rocket
Earthworm Jim
F-Zero: Maximum Velocity
Fire Pro Wrestling
GT Advance
Iridion 3D
Konami Krazy Racers
Pinobee
Pitfall
Rayman
Ready 2 Rumble Round 2
Super Dodgeball Advance
Super Mario Advance
Tony Hawk's Pro Skater 2