I used iTunes once and instantly fell in hate.
Foobar2000 is the only thing for me. It plays everything and can DO anything to anything else. If you think it, it probably does it natively or there is a plugin for it.
Since most people don't like the technical awesomeness that is FB2K:
Here are some alternatives [
list 1] [
list 2] [
list 3] [
link 4].