I attended a session on NoSQL databases at IndyJUG today. Tom Hunter, the presenter, had done a very extensive research last year on the entire NoSQL landscape for his personal project, and the presentation was a aggregation of this information - he managed to give a good overview of the different NoSQL databases and had a very interesting way of classifying them, if I remember correctly:
1. Column type databases - Hadoop, Big Table
2. Key/Value type - Memcache,..
3. Document type - MongoDB, Couch DB
4. Graph type - Neo4J