I just came across blinksale, an online invoicing web app, very nice, very smooth, produces a good looking invoice and is quite customisable. Combine that with 88Miles, an online time tracking web app and we might just have something here.

Imagine being able to track your time on a various project, hit a button in 88Miles and have it start up a new invoice for you in blinksale and vice versa, opening up an invoice in blinksale could provide a link from the invoiced hours to the breakdown in 88miles, all online!