Mac OS X: Music junkies looking for a full-featured, local-library program other than iTunes can rejoice. Enqueue is an attractive, lightweight player with a configurable interface, an "on-the-go" playlist mode and lots more.
If you're jealous of Windows' playlist-based players like Winamp or Windows Media Player, Enqueue is exactly what you've always longed for on the Mac. It's a full music library program that supports tons of music types -- including types iTunes doesn't support like FLAC and OGG -- as well as global keyboard shortcuts, Last.fm scrobbling, an equaliser and multiple library views so you can configure it to your taste. Plus, it can import libraries from iTunes and monitor your music folder for changes, so you can still use iTunes to manage your library if you have iOS devices. And, if you free your media keys from iTunes' grasp, you can even use them to control Enqueue instead.
Enqueue is currently in beta, and will be free until the final version is released. No word on price yet, except that it will be "reasonable". The developer is also still working on more features, like smart playlists, so if you find it too feature-light compared to iTunes right now, check back periodically and you may find it suits your needs better.