Inv24.com is an online web app which allows you to easily create and manage invoices. You just need to register, fill up the necessary information to setup your account(Company Name, Address, Bank account, Register number, Tax number, SWITFT / ABA, IBAN etc.) and you're ready to go.
Inv24.com is a nice alternative to complicated account software or inconvenient billing in Excel. Thanks to its user friendly interface, inv24.com lets you create great looking invoices in minutes. You can also create templates and then use automatic invoices to get rid of repetitive tasks.
Last but not least the service is entirely free.