I've been using Time Tracker for a while. It claims to be "a simple tool to keep track of the time you spend on any given task." Or you can "think of it as a to-do-list with a clock."

The tool is fairly easy to use: add a new task, assign it to a category [ this is optional ], then the clock starts to run. It supports multitask as well. This is a marvelous gadget to track how long you've been procrastinating. That's how I make most out of it.