Woot-off checkers are great to leave open as a tab in your browser because they automatically update and tell you when the next woot has started.
The trick is to find one that is stable!
Here is a list of a whole bunch of them-if you find a good one be sure to come back and post it!
Woot-Off Checkers Linky
http://www.strasburgtech.net/woot/v2/ i found this woot checker to be accurate and up to date and doesnt freeze all the time