i have to shake my head as I say this - I'm honestly surprised these choices worked out the best for me - but here we go:
Music: iTunes
Movies: Windows Media Player 11 w/ K-Lite Codec Pack
iTunes has an unfair advantage over other media players since my gf and I both have iPods. Still, it's easy to use, has a good search feature, can connect to other iTunes on the same LAN (awesome with flatmates and coworkers), and I really can't find anything wrong with it.
As for Windows Media Player 11 and K-Lite, the explanation is surprisingly simple: the combination flat out works. So far, they've easily handled every single movie I've thrown at them and they run fast & smooth. I tried VLC (with its built in codecs) as well as windows media player classic with codecs that I downloaded one at a time, and I always, always would run into a movie that I could not get working. With WMP and K-Lite, that just hasn't been an issue. Feature wise, they are nothing special. But they work, and for movies, that's all I need.