Web Search and Data Mining (WSDM)
Here's the program: http://wsdm2008.org/Program.html
The talks are avaialble on video: http://videolectures.net/wsdm08_stanford/
- the above link also gives a decent description of the purpose/focus of the conference.
"WSDM (pronounced “wisdom”) is a brand new ACM conference intended to be complementary to the World Wide Web Conference tracks in search and data mining. The pace of innovation in these areas has reached a level that requires more than one premier annual venue. Specifically, substantial work is currently being done in the areas of workload-driven crawling and monitoring, security and privacy, user profiling, personalized search and ranking, Web advertising, social media analysis, and spam detection.
WSDM is being co-sponsored by ACM SIGIR, SIGKDD, SIGMOD, and SIGWEB. "

The presentations were generally of high quality, and I'd like to single out this one as my favorite:
Finding High-Quality Content in Social Media.
Eugene Agichtein, Carlos Castillo (presenter), Debora Donato, Aristides Gionis and Gilad Mishne.