Along the same lines as MythTV, I use Snapstream's BeyondTV, another PC based PVR.
http://www.snapstream.com/ I also tried MythTV at the time, but I went with BeyondTV because they were the only ones at that time to offer automatically updating Canadian TV guide data. It supports multiple tuners (so you can record several shows at one time) and they just recently released a DVD plug in, which is nice because with one click you can burn shows to DVD. The best feature is the "smart skip" feature, which automatically detects the commercials in your recrodings and lets you instantly skip past them with a single click on your remote.
On this setup, I added a little Haupauge MediaMVP box on our other TV so that we could watch our recordings on either TV.
http://www.hauppauge.com/html/mediamvp_datasheet.htm
But if I were buying now, I'd probably just go for the Shaw PVR or TiVo...