Minecraft Creeps or the Skyrim Electronic Dragon Shout Hoodie.
If they actually existed, the Minecraft Creeps would come in packs of four at $4.99 a pop. The Skyrim hoodie, similar to Think Geek's other electronic clothing apparel, would run on four AAAA batteries (not included) and would be capable of reproducing all 20 of the Dovahkiin's shouts.
To be honest, we also wouldn't mind if the Star Trek Inflatable Captain's Chair or the Star Wars Admiral Ackbar Singing Bass were put into production. Actually, you know what, Think Geek? Just go ahead and make all of this stuff, we promise we'll buy at least one of everything.