I'm interested in speedrunning some GBA games that aren't on this site. Can anyone help me find a really good GBA emulator? I currently only have a (pretty bad) laptop, so I'd like to find an emulator that works really well with low-end devices. Any help?

Bizhawk with mGBA core. Check the Metroid Fusion and Metroid Zero Mission rules, they are the most refined for that emulator.

There really is no good alternative, not even mGBA standalone, I did some tests with it recently and its less accurate. You really only have 1 option for GBA emu.