If anyone is looking for a comprehensive accounting tool for personal finance or small business, GnuCash also has the ability to generate invoices.

In my opinion, the PDF generator made by OP makes way more beautiful invoices than GnuCash. However, generating is only part of the story; tracking invoice balances and knowing who still owes you is another. GnuCash does both in one place, which is why I am plugging it here. It's worked well for my small business. It even gives you a nice pop-up reminder when you open the program that reminds you about unpaid Accounts Receivable.