I looked around online, and found a few different solutions to the problem. One involved tapping the key with a hammer to get it to work, another involved drilling out the old cylinder to install a new one.
The biggest problem I found was that each solution was either temporary, expensive, or involved getting a new key. This means that you would end up with one key for the doors, and a different one for the ignition - not the solution I wanted.
This instructable will show you how I solved the problem. I ended up with a new ignition lock cylinder, but continue to use the original, programmed key. The total cost of the repair was the price of the part - $72.99 with tax. The whole job took me about 4 hours, but I had to figure out how a lock works without much help. If I were to do it again, it would probably only take 2 hours.
The repair involves changing the ignition lock cylinder for a new one, and reprogramming the computer to accept the new keys. Ford has a passive anti-theft system (PATS) where each key has a chip, and they have to be programmed in. No problem if you've got two functional keys, because you can add new ones, but you have to be able to turn the key in the ignition to do so.
Step 1: Stuff you're gonna need
#2 Philips head screwdriver
T20 Torx screwdriver
8mm socket and driver
small screwdriver (I used a small torx screwdriver)
small flathead screwdriver
clamp or vise
clean, light-coloured work surface
snap-ring pliers (might make the job easier, but I did it without them)
power drill and grinding bit
replacement lock cylinder (comes with 2 chipped keys)