Timebar ($2.99) has got to be one of the wackier utilities I've come across but it's one that may deserve to find a loyal audience.
It works like this: You pull down the menu, set a stop time and an optional audio alert. Click "Start" and boom, the menu bar at the top of your screen transforms into a progress bar. A blue line moves from right to left, providing a visual indicator of the time remaining.
Now, honestly, this app may not be for everyone. I found the moving bar at the top of my screen gave me a migraine (not a joke migraine, an actual migraine migraine), but I doubt this kind of motion sensitivity will affect most users. If you, like me, have carefully disabled every animation detail on your desktop (no bouncing icons, thank you, no window zooms), the app may not be right for you.
I thought it offered a cute idea and implementation. I particularly liked its "snooze" option. It's not expensive, and it's very easy to use.