Media Player Dot Net (MPDN), free and extensible
Media Player Dot Net looks like a twin brother of the classic Windows Media Player, it is written in .NET, and it takes advantage of several free extensions.
MPDN Extensions include two major components, Render Scripts and Player Extensions.
Render Scripts are similar to AviSynth scripts and plugins except they run fully on the GPU.
Features: Playlist support via extension — Output dithering — Deep color (10-bit and 16-bit) output support — Separate DirectShow audio and video graph chains — Playback rate control — Audio track selection — Video track selection — OSD — Subtitle support — Subtitle track selection — Chapter selection — Full / Minimalist UI mode (or anything in between), and more
Note that the player suffers from some driver bugs.
To use the player you need to download also a software certificate and install it (extract all files and run InstallCA.bat; you need to do this just once).