Although NoSQL databases like Hadoop(Apache Foundation),Redis(VMWare),Cassandra (developed and used by Facebook) or CouchDB get a lot of media attention lately, MongoDB appears to be the product to catch in this emerging market.
Making some search over Google trend and Job Trend(using indeed.com) looking for various NoSQL solutions but the evidence point out the MongoDB to lead those trend
SourceForge,Disney,Craiglist are all using MongoDB, check for full adopter list here: http://www.mongodb.org/display/DOCS/Production+Deployments
Google trend result for “MongoDB”
Job trend from indeed.com result for various nosql solution
Job trend from indeed.com result for “MongoDB”