Hunter - Find all the email addresses related to a domain
Look at that SaaS - Inspiration and resources for SaaS founders
AnyMailFinder.com - Find anyone's email address
Good Sales Emails - Best sales emails from great companies
RocketReach - RocketReach allows you to lookup email and phone for 250+ million professionals.
SaaS 1000 - Free exportable list of the fastest growing SaaS companies