I'm just using my modded Xbox running XBMC. All my movies are stored on my NAS that currently holds 500 GB. I love my NAS. It acts as a fileserver (obviously) but also as a webserver, ftp server, bit torrent downloader.
Here's a link to it. Note mine is the ds106e which is apparently discontinued now, so here's the new version. The company is fairly good with their firmware updates which is nice. What I like most is that it is much more energy efficient compared to having my PC running 24/7.