The Little MongoDB Book

Practical MongoDB notes with examples: CRUD operations, the aggregation pipeline, indexes, replication, backups, bulk operations, and drivers for Java and Python.

GoalKicker

A thorough survey of the NoSQL movement. It explains consistency models, partitioning, and storage layouts, then studies key-value stores, document databases like CouchDB and MongoDB, and column stores such as Cassandra.

Christof Strauch

A short guide to Redis and its data structures. It covers strings, hashes, lists, sets and sorted sets, plus expiration, transactions, publish and subscribe, and Lua scripting.

Karl Seguin