Blizzard Beach and Typhoon Lagoon both have several lockers stations seeing as practically everyone needs one! They do have two sizes though, like a normal one and a large one. I know the large is like $10, can't remember about the normal, not much less, maybe $8?
Animal Kingdom: *I think* are on the left when you've come through the gates, near the toilets and Guest Relations.
Magic Kingdom: Under the railway station - again they do two sizes (normal/large) at MK
Epcot: I dunno where they are in Epcot cos we've never had to use them
MGM: On the right-hand side as you enter the gates, there's a little undercover bit next to the shop, and there's loads of lockers in there
Downtown Disney: On the dock, down by the marina - but they don't operate on a key system - it's just a case of $2 (in quaters) every time you wanna lock it!
I don't ever remember paying more than $10 for a locker, and then you usually get most of it back at the end of the day when you return your key.
If you're going to Universal, it's helpful to know that some of the rides actually have free lockers (for like 1-2hours) for you to store your stuff while you ride. They are very handy if you don't have too much stuff. Rides that I can remember that have them are: Incredible Hulk, Jurassic Park, Dueling Dragons, Men In Black, Return of the Mummy