The Little Redis Book

Redis is a high-performance in-memory data store, similar to memcached but with a number of advanced features including more datatypes (strings, sets, sorted sets, lists and hashes), a pub/sub mechanism, various options for data replication and persistence and a number of other interesting and useful features. There's a new e-book about it that covers a lot in only a few pages, and is also free. Check it out: The Little Redis Book