The students enrolled in the Networks class I'm TAing have been posting very interesting material to the course blog. A good number of the posts discuss new software/services being developed which leverage concepts from network theory and game theory. These include your usual selection of search engines (see 1, 2, 3, 4), auction and advertising services (see 1, 2), social networking sites (see 1, 2, 3, 4), and analysis tools (see 1, 2, 3).
But perhaps the service that has has been most immediately useful to myself has been Freebase. In short, I view Freebase as an attempt to create a semantically rich, highly organized database full of user-generated content (very similar to Semantic MediaWiki). The course blog post (and the O'Reilly article linked from the blog post) provides a good overview of what Metaweb is trying to achieve with Freebase. As luck would have it, many companies keep an active eye on the blogosphere for reviews of their products, and Metaweb is no exception. After stumbling across the Networks course blog, Robert Cook was gracious enough to offer me an alpha invite to try out the current version of Freebase.
Freebase is built on top of Metaweb's other product (called Metaweb, no less). To quote Wikipedia, Metaweb (the product) is a semantic data storage infrastructure for the web. Metaweb exposes an API which developers can use to write software which can access the information. This is, in the end, how Metaweb (the company) intends to generate revenue, since other organizations seeking to use Metaweb for their own purposes will have to pay a fee.