Free invoicing. Badger writes it, emails it, and watches the due date.

Badger emails you about your own account — a brief each morning when something's happened (an invoice paid, an invoice gone past due) and a summary each Monday of what you're owed. Those briefs also point out what Badger could be doing about it. One click in any of them stops them for good, and it never affects the invoices Badger sends for you.