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I see a list here with a section titled M-theory - http://www.superstringtheory.com/links/reviews.html
In there these two look promising, http://arxiv.org/abs/hep-th/9607201 and http://arxiv.org/abs/hep-th/9802051
I would like to know if people have opinions of good starting points towards understanding M-branes and how they are used for constructing exact examples of AdS/CFT. [...I guess all exact AdS/CFT scenarios are M-theory constructions..]
Well, Becker, Becker, and Schwarz String theory and M-theory probably fits your description, as it has a lot of great text about AdS/CFT and it's relation to M-theory, etc. in the end.
Other than this, Lubos Motl also has an extraordinary summary of how matrix string theory works (if you can get the intuition, you'll see a relation to AdS/CFT) works here in this Physics.SE answer.