I've tried a number of software packages to run my media center kicking off with MediaPortal in the days of Windows XP when no suitable software was bundled but a huge amount of time and effort later Windows 7 with bundled Media Center came along and saved me.
Windows Media Center is not a perfect solution, too many forced adverts, too few rows of content with lots of empty space but it works out of the box. Luckily Media Center Studio helps and is tweaked nicely with Mikinho's Media Center Strips.
What I have found that since Windows 7 there are built in codecs for MP4 files from a Sanyo Xacti camera, quicktime for the Lumix TZ5 and laterlly support for AVHCD files from a Lumiz FZ100, all with no changes by me.
I have also been using MediaBrowser for Movie support and YAMM to pick up move details. Unfortunately, the music plugin crashes my machine which is a shame as WMC's Music library sometimes corrupts of its own accord so having a backup capability would be handy so Music Browser is on hand just in case. In fact I've just had another crack at the Music support on MediaBrowser but it just doesn't display my files reliably, I've checked all of the files to ensure I have tags in place on everything (and weeded out a few corrupt MP3s as a result too) but no luck still.
I also have in place MKV capability which makes life a lot easier for an movies, divx provides the basic codec capability and configuring MKV file extensions via MediaBrowser's External Players works nicely and combined with the integration of Cyberlink PowerDVD that game with the Samsung blu-ray drive for blu-ray disks everything works neatly now.
I did make a short foray into XBMC which looks great, miles better than WMC but configuration changes don't always seem to result in a working solution so blu-rays would play - WMC works so it lives on and the Neo theme in MediaBrowser looks fabulous so why tinker any further?