Got a case and wifi dongle for mine this weekend, installed Raspmc and connected it to a telly in our kitchen as haven't got round to putting an aerial socket there yet.
Works surprisingly well and can watch FreeView via TVcatchup and the terrestrial channels catchup services. Haven't got my head round how to tag my iTunes media for xbmc yet though.
Apart from the Pi I think I spent £5 on the case, £8 on the dongle and £7 on an SD card and use the free XBMC remote on my iPhone. I also needed an old USB keyboard for initial setup
If I'm honest though, I think I'd prefer an Apple TV there eventually but at the moment I have a perfectly usable and arguably more powerful device for around half the price.