Being self-employed means you'll have to do a lot of drab stuff you probably don't want to do, like tax returns, accounting, and invoicing. Luckily, there are lots of tools out there to make the job easier. For invoicing, my personal favourite is Invoice Home. It creates all your invoices on the same template, so all you need to do is add in the details and download. It will also keep a record all your past invoices and crunch numbers, which helps with accounting.