This is when I need the girlfriend to step in and stop my craziness!
SFF do rock, but have a good read and LONG surf before deciding what to go for. Aria can be good for comments and have a special on the SK43G (£116 inc VAT)
<-EDIT: They've just changed this to the SN45G for the same price! Wonder if they're clearing them out for new models?
The forums over at sudhian.com are good, but it appears the ITX SFF Shuttle can be a little crap when it comes to quality standards and customer care. Many over there are happy with their systems however.
The new MSI looks awesome (see below) for a front room entertainment box, however I'd still wait for peoples opinions first.
As for ITX, not too many stand alone motherboards. I've seen one for P4 and the rest are built in via CPU efforts. Some of the cases you can use look nice though!