Xine

A DVD, MPEG 1, 2, and 4, ASF and DivX ;-) player for Linux and likely other Unixlike OSs. Although in development at the time of noding, Xine is by far the easiest Linux based DVD player. The project aims to provide software only DVD decoding - this allows a much faster release time. As the website is hosted in the USA (at Sourceforge), where the legality of non MPAA licensed DVD players is unclear, the modules necessary to play encrypted DVD must be downloaded elsewhere. There's another project called Xineplayer which includes these modules, and is hosted in Russia.

Actually, there is also a Xine patch that allows hardware decoding through the popular DXR3 and Hollywood Plus decoder cards. It can be found at Sourceforge and though it requires some fiddling, it already works quite fine for me, at least the video out; the overlay is in a very early phase of development.