Media server, like a DLNA server? Surely not. If you're looking for a media player, Shuttle+ is pretty good. It downloads album art, lets you browse by artist, album, or song, and includes a 6-band EQ if you need it (although I'm not sure whether that's a feature specific to the DSP built into CyanogenMod or not).
You should be able to put your MP3s anywhere there isn't a .nomedia file, and Shuttle+ should be able to catalogue them. Download ES File Explorer just in case you need to do any housekeeping on your sd card from your phone.
Other notable apps: Soundcloud is nice when you get bored with your own music. Google Play Music offers a few free tracks every month. Freegal also lets you download music for free if you have a membership to a participating local municipal library.
Sent from my LG-VS980 using Forum Fiend v1.3.1.