Hi, well the best suggestion I can give is check out http://www.thegnomonworkshop.com/dvds/g ... int_g.html
now these dvds are not free but they are worth every penny! I love them and bought all of them myself as reference. Another suggestion is http://www.dylancolestudio.com
, and of course mattepainting.org is loaded with info and wonderful paintings of environments!
And here is a good book to own http://www.ballisticpublishing.com/book ... _painting/
but if it is a little on the pricey side you can find it on amazon.com cheaper! Here take a look http://www.amazon.com/Dartiste-Painting ... 146&sr=8-1
and here is a great book you should start out with first! (GET THIS BOOK!) http://www.amazon.com/Invisible-Art-Leg ... _b_title_4
And for digital painting in general here is a book http://www.amazon.com/dartiste-Digital- ... _b_title_1
All of these will explain Matte Painting very well. That's the best I can do. I hope that helps.