Hexbugs. They sent me and my family a bunch of bugs plus what they call a habitat and let me tell you these things were a huge hit!
We invited a bunch of kids ages 3- 5 over and we held bug races. We let them set up different "race courses" with the habitat and each kid had their own bug. The kids let the bugs go at the same time and cheered on as their bugs bumped along, made wrong turns, flipped over, righted themselves and finally won the race.
This toy was great for a party (would even be better for older kids). We let the winning kid keep their bug until each kid had won a bug to take home.
If you are looking for a good Christmas gift (you know the one that will beat out the others) Hexbugs might be it. My son really enjoyed it but what really surprised me was how much the girls loved it! One mother even called me the next day to say that her kid was begging to come back over and play some more with the Hexbug race track.