I've been trying to hunt down an awesome invoicing program for...well... ever since my second year at the Langara Professional Photo Imaging Program. Right now I'm using On The Job, initially it worked very well, it helped me track who had paid me and it sent out nice looking invoices (read as it looked better than the excel sheet I was using before...). The major issue I have with it is it doesn't sync to your Address Book and you can't run a report on how much you have invoiced this year, FAIL. It was a quick fix that served its purpose, you get what you pay for.
So now it's down to the final two contenders. In one corner we have Billings 3 and in the other we have iBiz. Billings 3 is just a nice slick UI with some great "blueprint" billing options, like if you have a set wedding package you know all your cost for one click and it's all there (assistant, shooting fee, travel, expenses etc etc). iBiz is nice in the fact that it syncs to a program called iBank which helps with expense tracking, something I'm always doing with Excel right now.
Stay tuned for who will be left standing after today's stress tests.