Mac: It's no secret that a lot of people really don't like iTunes, but that doesn't mean that most of us have bothered to actually replace it. If you really just want a simple way to play some songs from your iTunes library, iTunes-Remote is a command line tool that's simple to use.
iTunes-Remote still requires that iTunes is running, but if you're not a fan of the actual interface in iTunes, this lets you use the much simpler command line to control it. Usage is pretty simple, you can play songs, skip tracks, or search. Beyond that, it just does it job as simply as possibly. Sure, it's a little overkill as far as reductive features are concerned, but it's actually a pleasure to use, especially if you tend to spend time in Terminal anyway.