There are a few new cheap and sometimes FREE accounting tools that are part of the Web 2.0 explosion.
Blinksale is great for quick invoicing. I have used it to see invoices to my bookkeeping clients and it faciliates PayPal payments. The only downside is that you can only send three invoices a month for the free version. I suggest upgrading to the next level.
Freshbooks.com offers a similar service but it is not as efficient. More detail for clients has to entered, but they do offer to send in the mail an actual hard copy of the invoice.
Wesabe is more for personal finance but since many of my clients are micro-businesses, it’s a definitely worth a look.