There's no shortage of clocks and timers for the iPad. One of the most complete is Clock Pro for the iPad, which is on sale this weekend for US$1.99.
Clock Pro is an alarm clock and uses notifications so you can get that important wake-up alert without leaving the app running. There is both an analog and digital clock design, a chess clock, a world clock, sunrise, sunset and tide clocks, a sleep timer, an egg timer and a countdown clock. Most clocks can run full screen and are beautifully rendered. We took a brief look at this app last year when it was $5.99 and gave it a positive review. Now it supports multi-tasking, and it's 4 bucks cheaper.
A couple of caveats. The app can't wake you to your own iPod music if it is not running, but the app does allow you to choose among several different sound options if you are using notifications. Not all the clocks work in full screen, but otherwise this app does pretty much every kind of time keeping you would want. If you'd like a free version that doesn't multitask you can get it here, but I think the paid version is more useful. There is also an iPhone and iPod touch version on sale this weekend for $0.99.