For many self-employed people, invoice generation is a task that gets spread inefficiently between Word and Excel. Invoiceplace lets you shift the process online and get some automation happening.
Developed in Australia, Invoiceplace lets you create, track and send invoices and quotes. The webapp includes automated sending of invoices and can request payments through either PayPal or Paymate. There's also support for multiple currencies, potentially useful if you work with clients overseas. The navigation feels a tad clunky in an era where Ajax-style Web 2.0 interfaces are the norm, but most of the functions you'd expect are there (I couldn't spot any data import facilities for customers).
Invoiceplace is free for sending up to five invoices a month, which might be OK for a secondary business. Premium accounts (from $15 a month) offer much higher send-out levels and allow for greater customisation of the invoices themselves.