I assume by this you are referring to the buy one MH3U get one free. Or is there another way to get a free MH3U with a new purchase of a 3DS? (Wife has just got a machine, but not got MH3U for it)
don't forget, free monster hunter 3 unlimited when you register a new 3ds until the end of July
Free copy of NSMB 2 when you buy any 3DS/3DS XL. Black XL is Ł140, so with the game it's a pretty damn good deal.