Toprankblog.com has compiled a great list of 4 free and 1 partially free reports on using social media for B2B marketing.
Here are the direct download links for the 5 B2B social media PDFs, no sign-up required.
B2B Tech Marketing and Social Media
The Infinite Dial 2011: Navigating Digital Platforms
2011 Social Media Marketing Industry Report
Social Media for B2B Marketing