Gambatte works, you can grab it here:
http://maemobox.org/dblank/gambatte.zip

unzip and run from command line like this:
gambatte_sdl -i enter f4 f7 f8 up down left right -s 2 -r 44100 file.gb

key mappings:
dpad center = start
menu button = select
- = B
+ = A
with up/down/left/right as normal

Someone who isn't me should make a frontend