Toggl, free web-based time-tracking
Toggl is an excellent solution, offered in a completely savvy web 2.0 interface that gets you where you want to go. The site tracks time and lets you hit a toggl (whoa, go figure) button to start and stop your "billable hours" timer. I was a bit wary at first that toggl wouldn't offer a way to change the time it had recorded, leave you stranded with pushing the button every 108 minutes until you got the right amount of time, but my worries were completely unfounded. I was ready for something much harder than clicking on the box and reentering my own length of time.
If you think pie is easy, toggl is easier. Complete with a reporting feature and multiple projects, toggl's goodness clocks in (pun somewhat intended) at the right price of free. As you know, our motto here is one more happy cheapskate, or wait, I don't think we actually have a motto. I'll have to get back to you on that. meanwhile check out toggl, and you will never wonder if you charged your client enough for the hours you spent on that killer project.
Add "toggl" to your spell-checker, jack, and you won't be disappointed.