For a free piece of software, Windows Media Player is an excellent choice for managing your growing collection of video and audio files.
However to make the experience of using WMP complete you need to add a simple MPEG-2 Codec that will allow the software to playback your DVD collection too!
For more information on a suitable DVD Windows Media Player Codec for your PC's operating system you can read Microsoft MVP - Marc Liron's article:DVD Windows Media Player