YesGraph - Boost viral growth by recommending who users should invite
Invitation.Codes - Share the referral codes of products you already use and love.
NewsWhip - Chrome extension that checks how viral your content is
Best Referral Programs - A curated directory of startup referral programs
Promo Self Serve - Launch a promotion across the internet in 90 Seconds
ReferCodes - See your friends’ referral codes and share your own