In Europe conversions of popular NES games were the most succesful, like Castlevania and SuperMarioland. In Japan there were far more original games, like Bill And Ted's Excellent Gameboy Adventure (based on Chuckie EGG) and Yar's Revenge. Roms can be found on Retro HQ.
The GBA started out with Super Nintendo ports. And even these days Nintendo charges 15 euro for a NES-port. There are some great original games now, like the strategy game Advance wars (Pictured). This combines classical strategy with Manga-cuteness. Emulating this game has another advantage. One can save his two player game and mail it to a friend to have a great two player battle.

WarioWare is another highlight. You are a tester of a software company and have to play hundreds of little games, which last for 5 seconds. A site with PD-games for the GBA, like a conversion of the Spectrumclassic Skooldaze can be found here. On PDRoms there are conversions of a few other classics, like Elite and emulators that can make your GBA emulate other systems.
mario2
There are no links to commercial GBA roms, as the GBA is a current system.
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