A big thanks to DisneyAddict for this infomation:

Magic Kingdom free wifi is available on Main Street USA and outside the City Hall guest relations.

EPCOT - In the Lotus Blossom Cafe which is just at the back of the Nine Dragons restaurant in China. The signal seems to be stronger near the back of the cafe, it's called Warpdrive.

EPCOT - Innovations East near the Universe of Energy exit

Disney Hollywood Studios free Wifi is available between the Brown Derby restaurant and Mickey's Sorcerers Hat.

Blizzard Beach, free Wifi is available in the area close to the gift shop near the main entrance.

Downtown Disney - Inside Wolfgang Pucks Express

Downtown Disney - The cigar bar (Sosa Family Cigars) right next to Raglan Road, just opposite the Harley Davidson Shop. Pretty strong signal even outside the bar

Downtown Disney - Outside The House of Blues. There are a couple here

Downtown Disney - There is a cyber cafe inside Disney Quest with free Internet Access.