Cassandra Summit was just a few of weeks ago.
If you couldn't make it, the sessions and slides are now up: http://www.datastax.com/events/cassandrasummit2012/presentations
The sessions that I typically find compelling and fascinating are the user or war stories. At the Cassandra Summit, there were a good representation ranging from the small to the not-so-small.
One gem that you might overlook is the session by Eric on CQL3. Worth a watch.