BillGrid.com - BillGrid is an easy to use online invoicing, billing and expense management system that will save you time with tracking clients projects, expenses, invoices and payments.
FreshBooks - The ideal accounting software for small business owners.
ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.
Avaza - Beautiful Projects, Timesheets, Expenses, Quotes & Invoices for Small Businesses
Elorus - A super-easy online invoicing & time tracking software
Invoice2go - Full featured, invoice and estimate solution with full mobile support.