PowerDVD is by far the best DVD player for Windows I disagree. The best DVD player for Windows (and Linux) is VLC [videolan.org] It supports menus, surround sound (even DTS) and AFAIK all the other things PowerDVD does. But on top of that it is region free and allows you to skip the commercials and copyright warnings that PowerDVD forces you to watch :) It's also free as in beer and speech.
My dvd software trial was about to run out and I was wondering if I should renew it. I thought the playback was excellent, though I hated the user interface. I was also kind of annoyed by it as it would sometimes refuse to output digitally to my SP/DIF without rebooting. Instead it would decode the audio itself and output in stereo. Bleagh. I'm happy to say now that there's no need anymore. This software is fantastic! It's got a very clean, uncluttered interface. It plays DVDs perfectly (they look fantastic!!) and does what I want and doesn't touch the audio stream, instead allowing my receiver to take care of it itself.
And, as the poster said, it's completely free and available on like every platform. Free highly-quality software that is being actively developed and improved!!! If you want you can even get those disgusting skins that try to make DVD playback software look like an actual DVD player. So if you consider that a plus point for software like WinDVD/PowerDVD (i don't, they just confuse me) then you'll stil be satisfied with this. This is also a plus because I've been thinking about switching over to linux and using MythTV and/or this on my media center PC. Now that I know that this sofftware exists already on Linux, I'm a lot more comfortable switching.