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.
Avalara - Cut tax compliance costs, not corners. Avalara automates tax compliance and can help improve accuracy while reducing costs.
ChargeOver - ChargeOver automates recurring billing, subscription billing, & payment acceptance. A SaaS that integrates with Xero, Quickbooks, & has an API. Free trial.
TaxJar - TaxJar simplifies sales tax filing for eCommerce sellers.
MinuteDock - Web-based time tracking software designed to integrate with the Xero accounting package.
Thomson Reuters ONESOURCE - ONESOURCE tax software and solutions synchronize every aspect of your work and link international, country, state and local tax laws.