CoRepo - A free and open company search engine.
FullContact Card Reader - Automagically scan biz cards into LinkedIn/Gmail contacts
AngelList - Access top deals through investor-led syndicates
Clearbit Connect - Clearbit Connect is a free extension that surfaces actionable information on the people who email you.
Angel Match - A database of 94,000+ Angels and VCs to raise your capital
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.