I recently discovered a new time tracking tool called Toggl (you can visit at toggl.com). I needed something that I could use that was web-based since I do work from two locations (at my full-time job if I have down-time and at home). The nice thing about this is that the free version really doesn’t have too many limitations (you can even have up to 20 users). It integrates with Basecamp for the paid
version and also you can have billable hour rates in there and planned tasks. For me it’s perfect. They also have widgets for Mac/PC plus a gadget for gmail (http://www.toggl.com/toggl-gadget.xml). I have mine synced to my Google account so I can login without typing anything in.
It also has a desktop version if you need to work without the internet (you need internet access to import your settings and then when you want to update it to the internet).