Invoicing service of choice for freelancers?

Freshbooks is great.. I think the account is free as long as you only have 1 client at a time in the system

I use excel, due the fact we issue invoices few times a month (agency).

http://theanchorapp.com/ - this is a self-hosted free app. (not affiliated)

I use Harvest for time tracking and invoicing. The free tier is fine if you only have two clients at a time, and the cheapest paid plan is pretty affordable.

Use zoho invoicing solution. Templating is awesome.

Excel