iBiz is a great time and billing management app for those who are self-employed or otherwise might have a need for keeping track of their projects, right down to the minute and dime. It integrates well with Address Book and iCal for all your contact and todo needs, which is great, for example, if a client would like to see a published calendar of the time you've spent on their project.
iBiz also acts a bit like a file/project management dashboard, as you can associate files with a project in iBiz and automatically start timing you work when you open the file from within the app. Once a project is done, iBiz also offers a healthy array of invoice options, ready for print, PDF and/or email. Networking capabilities are also baked in, with an iBiz Server edition available, but I don't work in that environment so I don't have much to say on that end.
It looks like we haven't mentioned iBiz on TUAW before, but I can personally vouch for it as a great app since I've been using it for a couple years now. This latest update brings it to version 2.5 with better iBank integration and bug fixes, and also adds Universal Binary goodness. A 10-day demo is available, while a single user license will run you a mere $29.99.