Great article from Mashable: http://mashable.com/2008/07/17/social-media-for-business/
It provides some examples of "social media" for the business. I've summarized them below. Please feel free to add what you've done.
Introducing new employees via internal blog or rich profile (At Jive we encourage new employees to create an introduction blog post a week after they start)
Learning 2.0 (employees uploading short videos or podcasts to help colleagues learn something)
Sharing of recruiting "Best Practices" across global team
Sales collateral - via wiki, or central file store with comments
Lead generation - by creating a presence on LinkedIn or Facebook
PR - external corporate blog
Better Customer Engagement
Competitive Intelligence Library (both published & "heard on the street")
Thought Leadership - like Clearstep
Product / Design Group
Product Prototypes - collaborate in real time with 3D models in virutal worlds
Innovation - internal or external platform for ideation.
SME "email relief" - create a space that holds pages, discussion forums, blog posts and more to communicate expertise proactively, and to answer questions
Functional Design Documents