I'm particularly fussy about what a media player should do. For starters, a good media library is a must, with good ID3 tagging support. Also, flac support is a necessity, and it can't be too demanding on the resources, as I like to have it running in the background when gaming. Video support is nice, but nothing I'd look for, as I'm pretty happy with VLC for all my video needs. Oh, and one last thing, last.fm integration, while by no means needed, is also pretty neat.
So far I've looked at the following:
Foobar 2000 is pretty good, if you want a REALLY lightweight player. It seems to play pretty much any format I throw at it as well, which is nice. The interface however, is somewhat spartan. It certainly serves it's purpose, but the media library wasn't overly intuitive, and it failed to recognise a lot of the ID3 tags in my library. They do have a new version and website since I last tried it though, so it may be worth a look.
Songbird seems like a good open source alternative to iTunes. It also has a plugin system akin to firefox which is nice. Otherwise, I'm not sure what else to say, as I've barely played with this one.
MediaMonkey - This seems pretty cool, although I've yet to try it. It's another one that seems to follow the itunes format, only this seems to support a massive amount of filetypes. It also supports scripting, which could be interesting to play with. I'm always wary of products with a payware option though, however it does seem that most of the functionality I'd be using is available in the free package.
So, what media players do you use? Which do you find works best with gaming, and are there any that you would totally avoid?