This emulator is surely the best around for Windows platform. It's portable, so you just unzip it and you're done, without need of an installation. Second, it reads both GameBoyAdvance and Gameboy Color roms. It supports a number of display options (full screen, 2x size). Screen capture option, quick-save function.
Download link for VisualBoyAdvance 1.8.0 beta 2
Size: 618 KB