Stupid simple music player?

If you are looking for something lightweight than Rhytmbox, then try audacious

sudo apt-get install audacious

It is also present in Ubuntu Software Center. HTH

Personally I use moc in such cases. If you don’t mind it being in text mode, I recommend it.

You could use Totem, you can load/save playlists and it's pretty straight forward (and installed by default).

Edit: You might also want to have a look at XMMS, which is pretty similar to WinAmp.