Computers are great for many things. While I am not a big fan of fully featured, complete accounting packages like Quickbooks or Peachtree (very rarely do I meet a Business Owner who actually uses more than the check writing or invoicing modules), I am a fan of a good online invoicing applications.
I usually recommend Freshbooks to my clients, but the new Curdbee looks to be worth checking out — Especially because it is free!
This application seems to be directed mostly at those incvoice via paypal or google checkout, but a user can still print out mail an invoice.
I’m keeping my eye on this one.