I went for a prebuilt system for my HTPC
I had tried NMTs like the Popcorn Hour and Istar, but the lack of XBMC style graphics just left them lacking something,
Tried several PCs, till I found a Medion at Aldi that hit all the buttons
Quadcore Intel CPU - 3Gb Ram - Nvidia Graphics with HDMI - DVI & Component Outputs (Freeview and Sat Tuners built in) X10 Remote and the real deal maker, an ESata Hard drive bay on the top that you can plug in 750Gb Esata drives with no hassle just hot swap and off you go (I already had a 2Tb NAS), and with 10 of the 750gb external drives that covers my needs for the next few years! (Excessive I know but Aldi were selling the 750gb hot swaps off at £49.99 to get rid of them, so it would have been rude not to!)
PC was £469 with 3 year warranty, its whisper quiet and XBMC has never been so good. May not suit all but fits my needs like a glove!