Maybe this is a bit excessive, but if you've ever forgotten about a cup of tea you will find this program a lifesaver.
Cuppa is a free, tiny MacOSX program that you run just after you make that cup of tea. It runs in the dock, counting down the seconds until your tea is ready. And when it is, a window pops up and a noise sounds to alert you that your tea is ready for consumption. It comes with a few preset brewing times, and you can customize it as well, for your favorite brew.
So, bid farewell to the days of frustration and cold, bitter tea. That is, if you remember to start up Cuppa.