Simple Invoices - Never Wait For Clients To Pay You Again!
Slimvoice - Insanely simple invoicing
Upcount - Invoicing for freelancers & small businesses
Zoho Invoice - 100% free online invoicing software for small businesses.
Invoice Ninja - Invoice Ninja is a free, open-source solution for invoicing and billing customers.
Inveezy.com - Inveezy is a free invoicing website with no login.