iTimer - the One-Touch timer for the iPhone and iPod touch. Load the app and the timer starts counting down immediately - use it for a powernap, timing games, cooking food, anything you like that you need to time! In addition to the countdown timer, it also shows a discreet digital clock - which can also be displayed full screen with date as well!
You can of course change the time duration and the alarm sound, turn autostart off, and if you want to you can also post your status to Facebook. You can also set it up simply to use as a large digital clock.