Executive Summary: it's Alarm Clock for OS X.
I happen to live in a two storey house where my office is about as far from the kitchen as it's possible to get (i.e. the kitchen is on the ground floor a long way from the stairs, my office is on the top floor a long way from the stairs). So, I'm always burning stuff in the oven or making coffee or tea and then forgetting to drink it until it's no longer drinkable. What to do?
Macs used to have a really neat Desk Accessory called Alarm Clock, but it didn't make it into Mac OS X, so I ended up writing my own, losing the code, and then doing it over and over. So, here's my solution for your cookie baking, coffee brewing, tea steeping convenience. It's free to a good home.
Download EggTimer 1.0 (Mac OS X Universal Binary)