In continuation to my exploration on NOSQL arena, after cassandra I'm following with Mongo DB which is much lightweight than cassandra which also follows the Document based approach. In the quest for finding more information about the same and learning it fast, I had come across some good resoruces, which you can refer too.
There are very good resources available at Mongly.com
Very good one for anyone who would like to kickstart MongoDB without getting to know more about it. Learn MongoDB by doing through an tutorial which you can work through. Very interesting and good one too.
Learn from master themselves on the MongoDB User Manual from this link:http://docs.mongodb.org/master/MongoDB-Manual-master.pdf
Also you can check the Little MongoDB Book by Karl Seguin who has made it simple to learn MongoDB with analogous comparision with DBMS. http://openmymind.net/mongodb.pdf
Thanks to Chris Kite for sharing wondeful presentation on mongodb in this URL: http://www.slideshare.net/chriskite/intro-to-mongo-db . very good one for begineers.