A redirector client so WinAmp can access music on the PC. Right now there are about 6 solutions, but none of them are feasible for most people. They either require a complicated installation, lack genre sorting, basic folder listings only (no meta data), incredibly slow, or require equipment to work (NAS). See below for the existing crappy solutions.
I have searched high & low, and my basis for reference now is the Synology NAS solution with DS Audio. If there were a way to remotely gain access to the PC that contains the respository for your music (Home Server, PC, NAS, etc), & play it on your phone.
Personally I hate syncing new music to my limited storage phone each time I want to change things up. I know there will be a solution soon with Windows Mobile 7 & Windows Home Server version 2.0 (Vail), but that's months & months away; not to mention a non-ubiquitous platform.
Ampache - Too complicated for average user to install
Subsonic - No Genre sort & no easy playlist inclusion
Jinzora - Too complicated for average user to install
AudioGalaxy - No Genre sort & no easy playlist inclusion
Orb - Insanely slow
Synology NAS - The absolute best solution I have seen so far. You install an app called DS Audio & DS Photo on your phone, you have HUGE buttons to sort/view your music, and it's super fast.