ITunes sucks, it still uses more CPU then mostly any other music player.
I use Winamp, it's small, easy to use, little CPU use, and well, there are games where you can download special programs where you insert an operation into the console, and it changes the song or the volume, or whatever for Winamp. There's one for FL, I think.
I have the last version of winamp and it does not annoy me with registration.
registration is only for burning CD and DVD at full speed. But as I don't care about that it does not annoy me.
WMP 11 on the other side, sucks badly. It wants me to register my copy of windows, and also phones home sending a lot of private information that I don't want it to send. I had to remove it the hard way as it didn't want to go unless I activated my copy of windows. It was the worst player I've ever used in my whole life. The only reason I use WMP is to see HD-DVD movies. That is because WMP uses my video card to decode the movie instead of my CPU.
(If you find any mistake in my English, please let me know via a PM)
(Really, I speak terrible English, so please, tell me if I make mistakes. I'd like to improve it a bit )