Broken/Spare Keyboards: I would recommend finding at least 2, maybe a 3rd to break down for extra vowels to use. Its amazing how gross these things can get...I consider myself a filthy filthy human being after examining the underbelly of my keyboards!
Magnets: found a 50 pack at Michaels for a couple bucks - they are about the size of dimes
Glue Gun + Glue Sticks - I used about 2 small glue sticks, it didn't take much
Flathead Screwdriver (use as pry bar) - you could really use anything for this..its not a gentle or careful process by any means
Step 1: Pry Out the Keys
Step 2: Glue the Magnets to the Keys
The shape of the keys actually works very nice because it captures the little glob of glue in its empty under-chamber. It allows them to adhere very well and give them a solid feeling when moving them around the fridge.
Step 3: Commence the Tom-foolery
Keep in mind you can do things like flip Ms and Ws, use Zs instead of Ss, use Is for Ls, etc. Also, you can spell things out scrabble style to utitlize the same letter twice, plus it looks neat!
It really makes you appreciate the speed at which our fingers can type...it takes forever to spell out instructables with these babies, theres so many letters...not to mention they get mixed up and you have to use the good old Hunt N' Peck system!