Yes! These devices are known as flashcarts or flashcards. There are three GBA flashcarts on the market worth considering:
- EZ-Flash Reform. The EZ-Flash Reform is least feature-rich of the three flashcarts on this list, but it's still compatible with almost all GBA games (as are the other two). However, it does not support RTC (Real Time Clock), so games like Pokemon Ruby, Sapphire, and Emerald won't have time advance in-game. You can, however, patch their ROMs to partially compensate for this; when patched, the in-game clock will move forward while you play, but not while your GBA is turned off. (Side note: the EZ-Flash Reform is a modified version of the now discontinued EZ-Flash IV. The EZ-Flash IV is the size of a normal GBA game, but the Reform comes with two shells - one to fit inside a GBA's cartridge slot, and one to fit in a DS Lite's GBA slot without sticking out. The two otherwise have the same functionality.)
- EZ-Flash Omega. This card has more built-in features than than the Reform, including built-in RTC support, save states, and built-in Gameboy (Color) and NES emulators (the Reform would require you to download emulators separately).
- EverDrive-GBA X5. This is the most expensive of the currently available GBA flashcarts. Of the three flashcarts, this one draws the least power (thus maximizing battery life). It has RTC support, as well as built-in emulators. However, the EverDrive lacks the save state feature that the Omega has, and it's the largest of the three; it'll stick out of the GBA cartridge slot a bit.