* Provider (my library's "manager class")
* Config class (for managing user settings)
* Listener system (for fading sounds that are further away)
* MusicPlayer class (wish list)
I've never really enjoyed audio programming (especially since I don't have much experience), but it wasn't too bad. The hardest part was getting streaming working. It supports WAV and OGG files for sound effects and OGG files for streaming.
I'm contemplating going ahead and adding networking support and updating my engine system to accommodate. IMHO, 99% of games can benefit from multiplayer capabilities (be it co-op, versus, or MMO), so it'd be beneficial.