I find InterVideo WinDVD to be really nice. Simple! Easy to use, isn't loaded down with a beautiful GUI either so it shouldn't hurt your performance to much.
anydvd+any media player, preferably VLC or MPC, or sometimes WMP10, which I also like. All that windvd/powerdvd/any media player w/ "dvd" in the title crap have onboard decoder emulators, which are outdated and silly imo. anydvd decrypts the stream between the drive @ the chip, so your OS never sees it as encrypted, meaning any player will work.