Media Player Classic is an extremely light-weight media player for Windows. It looks just like the good-old Media Player v6.4, but has lots of nice extra features.
MPC has, for instance, a built in DVD player with real-time zoom, support for AVI subtitles, QuickTime and RealVideo support (requires QT and/or Real player), and lots more.
Download: Windows 2000/XP Version | Windows 9x/Me Version