[1] http://www.jriver.com/ [2] http://www.jriver.com/download.html
I haven't tried most of these, but Ecoute is well done.
Some hopefully helpful links:
http://www.hydrogenaudio.org/forums/index.php?showtopic=7726...
I didn't realize that it was multi-platform. Anyone on KDE should definitely install it, but apparently it's more widely available than that.
Simple, efficient, plays a wide range of formats (including FLAC, APE), auto-scans music folders, etc.
Vox is lightweight and can read a ton of file formats, as well as load up your iTunes library. I think you can set it to auto-load a directory at launch as well.
Audivarna is also supposed to be pretty good.