XBMC Media Center is a media player application developed by the XBMC Foundation, a non-profit technology consortium.XBMC is free and open source software available for multiple platforms, featuring a 10-foot user interface for use with televisions and remote controls. It allows users to play videos, music and podcasts as well as browse and view photos from local and network storage media and the internet. Says Wikipedia about it..
It is the best media center application as far as i searched.. I am also using it as a media database by fetching movie and music data from online sites like imdb, allmusic. There are a lot to write about this software but all i have to say that this one is perfect and getting better..
It has DLNA support for all your devices, to be served by xbmc also. You will not need any other serving software. It is also visually marvelous and is skinnable (even you can create skins if you want).
There are lots of plugins to connect to online video services in lots of ways like you tube, facebook etc.. And there is this plugin which i like most which is the subtitle finder plugin.. With this plugin you can directly search several subtitle sites while playing a movie and find exact matches for your movie in seconds. Because it is open source if is FREE and i think it will keep on growing..
Go quick: http://xbmc.org/