There are some widgets that are plain simple and super-useful. Minutes is one of them.
Minutes is a nifty countdown timer that alerts you at a specific time (e.g. 18:31) or after some period of time has passed (alert me in 7 minutes).
With just a few clicks you can control what should happen when the time is over: Launch an AppleScript or Application, start a playlist from iTunes, or just play-back an alert-sound.
This is one of the very few widgets where running multiple copies might make sense: One for tea, one for pizza, and one for the laundry. Of course you can choose between four different color sets to distinguish your clocks.
What's missing is just a little button to postpone an alert for five minutes...