I just discovered Freshbooks. They call it, “painless billing”.
The site provides an easy way keep track of billable hours and invoicing clients. With a free account you can have up to three clients.
It looks pretty cool. If you are a small firm or freelancer and you work with client- billing them by the hour this may be very good option for you. I believe in having the right tools to do the job as opposed to being cheap, unorganized and unprofessional.
Anyway check it out:

You can also check out Time59 (www.time59.com). You can have an unlimited number of clients for only $19.95 per year. There is also a free 30 day trial. It is designed for one-person shops.
Hey,
Thanks for mentioning us (FreshBooks) on your post. I always get excited to see people noticing all our hard work!
Saul
Head of Magic
FreshBooks!