I use SageTV. I have 250GB set aside for recording on my Windows Home Server. Honestly I really just download whatever I want to watch, then keep it forever. I rip 1:1 copies of blu-rays and keep them on there too.

It has 6TB of storage, and I'll probably be doubling that in the next month or so.

Honestly though, for $99, SageTV is quite nice. You can buy extender boxes to use on other TVs in your house that will play HD content from your HTPC.

Version 8 should be released Soon<tm>. I'm not sure what the current pricing structure is, I know I had to pay like $30 to run the beta version of 8, but it's been worth it.