The thumbpad on my Gamecube controller came off leaving a sharp plastic stick on which to give myself blisters. I've looked all over for replacement thumbpads, but they're no where to be found. I found a product called GelTabz at GameStop for about $5, but their pads didn't fit on my NGC controller's stub.
I decided to coat the stub in rubber myself, I Google'd for liquid rubber for a minute before remembering an Instructable called Rubber Origami by BlightDesign. That's where I got the idea to use Plasti Dip.
The 2 coats of Plasti Dip made playing with my Gamecube controller much more comfortable, but still a little irritating to my thumb after a bit too much play. I think I might try another coat or two in order to get more padding around the rim of the joystick since it's still a little sharp. I'll update this Instructable when I do, but it might be a while since I just moved and doing this on my couch and floor is a little bit of a hassle.
*Added 3 more coats, definitely a lot better. I wouldn't try doing 5 coats all at once, but maybe do 2, then do another 2 after 12 hours. 4 should be fine, I only did 3 more cause the first time was a little thin cause of the troubles I had.
CVS - or any drug store
Cotton Swabs - $3
Isopropyl Rubbing Alcohol - $2
Home Depot - or most hardware stores
Wire, 18 Gauge Aluminum - $3.50 (Optional)
Plasti Dip - $7.50
Please read the MSDS (Material Safety Data Sheet) for Plasti Dip. The fumes are a bit much so open a window and be careful of any sparks or open flames because it is flammable before it dries.