NoSQL = Not Only SQL
Tokyo Cabinet/Tyrant, Redis, Voldemort, Oracle BDB
Content caching (Focus on scaling to huge amounts of data, designed to handle massive load), logging, etc.
Strengths: Fast lookups Weaknesses: Stored data has no schema
Column Family Stores
Cassandra, HBase, Riak
Distributed file systems
Strengths: Fast lookups, good distributed storage of data Weaknesses: Very low-level API
Web applications (Similar to Key-Value stores, but the DB knows what the Value is)
Strengths: Tolerant of incomplete data Weaknesses: Query performance, no standard query syntax
Neo4J, InfoGrid, Infinite Graph
Social networking, Recommendations (Focus on modeling the structure of data - interconnectivity)
Strengths: Graph algorithms e.g. shortest path, connectedness, n degree relationships, etc. Weaknesses: Has to traverse the entire graph to achieve a definitive answer. Not easy to cluster.