I've used foobar2000 for a few years now. It's perfect at what I want it to do, play music. I don't want visualizations, I don't want to play games or watch videos, I just want a music player with a small footprint that can manage my library.
For smaller, one off plays, I use Billy. It's footprint is about the size of the mp3 it's currently playing. It's a bare bones player with no frills, but it's a great mp3 player:
Billy - Sheep Friends