The number of vendors out there able to merge your email and customers lists with social data is shrinking. More and more social media platforms are adding privacy settings to reduce the spread of this information. Flowtown and Rapleaf don't appear to provide social profile information anymore.
The single standout in the industry appears to be Fliptop (who have also purchased Qwerly). Fliptop converted its business late in 2011 to just doing social intelligence enhancement. Fliptop gets its data from a variety of public sources, and combines it to form user profiles. All the information gathered is public and can be found on the major search engines and business directory websites. Fliptop also integrates with Salesforce Data,
The only additional resource I've found is NetProspex. NetProspex allows you to upload, cleanse, enhance, share and download data. There are some small services like PeekYou you can do lookups with, but none appear focused on pure email enhancement like Fliptop.