Once tried the non-ambiguously named app Music Player, but the ads at the bottom of the screen have gotten annoying, also, the UI is pretty mediocre.
I tried a few others as well - Pi Music Player is great but the UI has a great bug where I can't navigate to the left of the top-screen menu, at least that I can figure out.
Currently I am using PowerAmp and it satisfy my needs. There are various settings and getting the pro version is definitely worth it. Especially if you want to change encode settings and output via bluetooth. Ogg support and "folder.jpg support" works really good.
Anyone have recommendations? Which Player are you currently using?