I usually use Rhythmbox, it has some great features - particularly the simple "add to play queue" feature and it's not clogged up with crap features that aren't worth my time.
The only problem is the sound quality seems to have just gone really shit recently. It's only with RhythmBox that this happens and it sucks because I use headphones a lot and, when I'm not, I still have a great speaker system. There must be something wrong with the settings or something, but figuring it out seems like too much hassle.

I've started using Songbird a lot now. It's a bit too 'complex' for my liking but I do like the fact it automatically connects to MP3 blogs and you can download interesting stuff with a click. I've found some great music that way.