My favourite ThinkGeek "joke becomes reality" April Fool's is the Canned Unicorn Meat
They actually got a for-serious cease and desist letter from the National Pork Board
for that. And then they eventually made it into a real product.
Possibly the entire kerfuffle provided inspiration for this year's Angry Birds Pork Rinds
ETA: Archive of past ThinkGeek April Fools
. I kind of want those Tribbles 'n' Bits. And a Monolith (in)Action Figure.