Windows Media Player 11 out now
It's been in testing for a while and I can't live without it now (on Vista) - though I expect I'll be a Zune marketplace man in a little over 13 days :)
If you have XP, you should check out WMP11 though as there are some very cool features such as the search interface and album art interface which I think iTunes has recently taken some guidance from. I know, weird role reversal eh? :)