There is no MIDI solution for OpenAL that I'm aware of. If you need MIDI (through JavaSound), you can use Paul's Sound System or another MIDI-capable library.
Slick uses MOD files for "tracker" audio, instead of MIDI.
MP3 is not a viable choice because of its commercial license.
I don't know of any decoders in Java that support MP3, let alone something that will be easy to implement in OpenAL. Besides, MP3 is a horrible codec for games -- poor quality, high filesize, gap of silence at the beginning makes looping more difficult, etc.
Best to just stick with WAV, OGG and MOD. Cheers!
