One of our most recent gems in the web 2.0 services pool, has to be SideJobTrack. The site offers a free service aimed at small teams web design teams and freelancers. It covers everything from time management, quoting, invoicing, clients and projects. We have looked at many similar, both hosted and standalone (free and paid) and this is by far the nicest, most intuitive sites out there. There is mention that at some stage the developer will be adding a paid version of the service, but the free version will always remain.
After only using it for a little under a week, it has already saved us an enourmous amount of time with keep track of all of our projects, predefining all our services, keeping track of time spent on each project and of course the full templated invoicing engine! All of this bundled together, full of ajax goodness!
Anyone looking for a similiar service should definately check it out.