I think you need to decide if you want a single box to record TV and store DVD's etc. If you do then you're looking at a media PC. I've looked recently and I couldn't find a single box that did what I wanted (TV tuner, record off air, networked, media store) but I may have missed something.
For the last 4 years I've been using a Windows Media PC which is very good. It's networked so I can record from TV onto it's hard drive and play back on a lap top anywhere in the house. It's just getting a bit slow now so can't cope with hi def, so I've just replaced it with a new motherboard, a single core Atom but with the Ion graphics chip, which can cope with all the hi def stuff. This is a small mini itx board, with no fans so the only noise is the hard drive, which is nothing.
I'm currently trying mythTV (which is free) which is a linux version of Windows Media Centre.
This is the motherboard.