Monday evening my mother mentioned her car key was broken, I measured the broken parts, printed up two prototypes, and printed out a fully functional replacement the following morning.

If you need a similar key fob replacement, use the "key4f.stl" version. The rest are if you want to tinker with them. :)

The saga of the replacement key fob:
http://blog.makerbot.com/2010/11/16/makerbot-hero-car-keys-part-i/
http://blog.makerbot.com/2010/11/16/makerbot-hero-car-keys-part-ii/
http://blog.makerbot.com/2010/11/17/makerbot-hero-car-keys-part-iii/
http://blog.makerbot.com/2010/11/17/makerbot-hero-car-keys-part-iv/
http://blog.makerbot.com/2010/11/18/makerbot-hero-car-keys-epilogue/

1) Print
2) Place electronic key beeper and key inside new key case
3) Snap case shut
4) Replace screw to hold key in place