Premium pack = 20GB HD/Wireless Controller/Headset etc
http://www.powerplaydirect.com/asp/itemdetails.asp?prodID=1245959
Premium pack (Full fat)
http://www.powerplaydirect.com/asp/ViewSectionItems.asp?currsec=ac&sID=84
Premium pack + 1 game
http://www.powerplaydirect.com/asp/itemdetails.asp?prodID=1245960
Core pack (Pleb/Cup spec)
Powerplaydirect is the cheapest in the UK at the moment.
http://www.xbox360searcher.com/buying.aspx
Worth a look.
BTW Just spotted this bundle, seems a good price:
http://www.sendit.com/game/item/6000000003559
Xbox 360 Console Premium Pack + Project Gotham Racing 3 + Xbox 360 Wireless Controller (Xbox 360) £269 delivered.