My little boy has got one of the little Hexbug nano's and he loves it, I can't find this for less anywhere else. It includes 2 nanos which are usually about £9 each. they also have other Hexbug insects on sale.
The Habitat set is a maze of interconnecting runs, corridors and pools that are ideal for a bunch of borderline-psychopathic vibrating robot bugs to run around. Even better, there are two rare Nanos included to get you going. It's even more impressive when you bung a multitude of them in there, though. You'll watch for ages as they flit off into corridors, climb over each other and generally get in the way an awful lot. Madness, really, but fun madness.