RocketReach provides real-time verified data for 450 million professionals across 17 million companies, worldwide.
RocketReach is very user friendly, and generally their data is high quality. We like that it marks personal emails so you can assess whether it is appropriate to contact that person there.
Adapt is a B2B contact and company database provider across multiple industries. Adapt has 100 million business contacts, including industry-specific company database and contact information such as job title, direct dial, and email addresses.
It's affordable and they seem to be able to find a wide range of contact details. They have a nice Chrome extension which works well.