The Perfect Egg Timer
Developer: Mirko Muller
Price: 99 cents; Buy it here
Why it's worth it: This is cheap, ridiculously easy to use, and the results of my egg-cooking experiment were a success; the egg came out perfectly cooked, as advertised. Though this is a very simple app, there's a kind of "window to your egg yolk" that lets you track the firmness as it cooks, in case you want to bail early for a softer yolk.
Drawbacks: This calculates times only for soft- or hard-boiling eggs; if you're looking for timing for overeasy or poached, you're out of luck.