This review is from: Crowdsourcing For Dummies (Paperback)
Customer review from the Amazon Vine Programme (What's this?)
This is a good introduction to the subject. It is well written, clear and easy to follow. Obviously as this is a `for dummies' book it only covers the basics. However it does do a very good job of this.
As it's a fast moving field some of the companies and web sites will have gone out of business and new ones will have emerged.