I don't care about "NoSQL" - I like Postgres and SQLite. What makes the individual "NoSQL" databases interesting, though?
Redis is in a design sweet spot, IMHO. The pure key-value stores seem way too low-level to me, but the support for atomic operations on lists, sets, etc. in Redis is very handy. It also works well as a cache for other databases, and newer commands like BLPOP are very cool.
While I haven't used CouchDB much, its model is also interesting, and I can see its trade-offs being an excellent fit for certain problems (just not mine).
"NoSQL" is about as useful as rallying behind "languages without camel-case" (NoCC!).