quod libet
Earlier I dismissed the quod libet music player since it needed 20% of my laptop's cpu to play music. The new version has been improved, it only needs a still exorbitant 13%, but at home I use my shuttle PC for music now, so CPU usage doesn't matter. And I think quod libet is worth the slightly lowered battery life on the road too.
There's no end to the features -- and plugins full in all kinds of interesting edges (onscreen display, audioscrobbler, alarm clock) -- and while it's still under development with a rough spot here and there, mostly around the plugins, it mostly just works.
I'm especially impressed at how powerful the tag editing is in quod libet. It makes it so easy to clean up the missing and broken metadata in even a large sound library like mine, and the effects are so immediate and nice as things get sorted into the right place, albums ordered as missing track info is added, album covers displayed, that it's addictive just to putter around in there.
Some other features that IMHO make it worth using include the ramdom album plugin, which lets it pick a new album at random when it finishes playing the current one (my collection is too varied and big for random track play to work, but this, mostly, does), the gorgeous album list, and the queue, an odd little feature that lets you insert any songs you like into a play queue, to play after the currently playing song. Which solves a lot situations I've been in before.
And the little details are all there too, little things like right-clicking on the play button to turn off the music player after the current song finishes; and automatically and quickly finding new music on startup; and properly supporting multiple artist albums.
And that just scratches the surface of things I've found to like over a day.. there's a whole regexp/tag based search engine in there, a music prefernces learning system with weighted playback, internet radio, playlists and more. And it's actively developed, and kinda oddly marketed squarely at Debian users.
Buh-bye rhythmbox..