50 Social Sites That Every Business Needs a Presence on

50 Social Sites That Every Business Needs a Presence on - Inside CRM http://ping.fm/oHsLk

Of course, the popularity of site change over time.  I'd add a few new B2B websites to the list: such as  MerchantCircle,   FastPitchNetworking,  PartnerUp,  and HubSpot.