analyze.email - Test the spam-y-ness of your emails
Clearbit - Clearbit provides Business Intelligence APIs
Canned Emails - A minimal site with prewritten emails
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
DeepMail - Diligently sourced emails. Accurate emails for Startups and established companies
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.