I've used J River Media Center for quite some time now (v12, but I know they just reved to v13)
I really like it's tagging functionality (very easy to batch tag MP3's, etc), and it also supports integrating with TIVO over HMO, which is very nice.
It costs a few $, but their support is pretty good, and their forums are quite active.
It's also somewhat programmable (you can write plugins pretty easily).
It's also got a full "theater" mode if you're running it on a media PC in your living room, but I don't do that so I've never really used those aspects of it.