I've switched to using foobar2000 (http://www.foobar2000.org/) and I think it's the first music player that I actually like. It's extremely simple and I've found it quite fast and responsive, even on my netbook.
I'd also strongly recommend foobar2000. It's incredibly fast, automatically adds music pretty much as soon as it's in the directory, is extremely customizable, and can look really, really nice. It has customizable global hotkeys, addon support, but works well out of the box.
If any one is still trying to use iTunes on Windows, I strongly urge you to at least try foobar2000. Once I switched, there was just no way I was going back to iTunes. It alleviates so many of the stupid daily annoyances I had with iTunes.
If you're in the one of lucky countries (or have credit card from one of them) I'd suggest Spotify, their client is marvelous (the best UI for a music player ever and also very fast), supports playing local files and since last version also syncing with Apple devices (maybe some others too, haven't had occasion to check).
For someone who'd want to switch from iTunes for higher performance and simplicity, rather than just going for an equivalent, what would I do?