What is the best recommended book on Bayesian Non parametric approaches ? Specifically something which also tackles regression problems such as Gaussian processes.
Don't know about books, but the following are very informative tutorials by two of the leading scholars in bayesian nonparametrics,
Ghahramani, Z. (2005, July). Nonparametric bayesian methods. In Tutorial presentation at the UAI Conference. (PDF)
Yee Whye Teh also has a great tutorial,
Yee Whye Teh (july 2009) Bayesian Nonparametrics in Document and Language Modeling
EDIT : Ghahramani gave a talk in NIPS 2011,
The best book for Gaussian Processes is Gaussian Processes for Machine Learning, of which there's a free pdf online: http://www.gaussianprocess.org/gpml/. For most other aspects of Bayesian Nonparametrics, like the Dirichlet Processes and the like, there are a few books that are essentially collections of papers from the literature, but they're not really text books to learn from unless you have some background already.