ca19lawyer2:The two heavy duty contracts treatises with which I'm familiar are Corbin on Contracts and Mc-somebody or other (McCormick?).
Corbin's treatise is indeed a widely respected one. Farnsworth is another, and is one that I happen to have. They aren't cheap, but are excellent for practitioners. Both also, I believe, have student versions of their treatises that are not quite as comprehensive but much more affordable.