A long time ago, I had a gift certificate and I couldn't find anything cool to use it on. I ended up ordering this giant mylar balloon blimp with a remote control and little propellers that could fly around the house. The thing was cool in theory but I quickly found that it was near impossible to ballast correctly and any draft from a fan or your cooling system would send the thing crashing into something. I suspect that as cool as the Air Swimmers are it would be just as hard to control.
The Air Swimmers don't look like a blimp though, these things come in two styles with a clown fish and a shark. Some people will recognize them as Jaws and Nemo. These things move around in the air using only their tails, which is pretty cool. You can apparently find them in some stores and you can order them online too. At the time of writing the ordering site direct from the makers was down due to high-loads and the store selling them is out of stock.
Both the shark and the clownfish have the same IR remote control. You can control the climb and descent of the fish along with the tail fin. Wireless range is up to 40-feet and both of the versions are 57-inches long and 36-inches tall. You will need a large room to have fun with these. All you can do for now if you want one is keep an eye on the website for them to come back in stock.