The leading treatises in the field are Scott on Trusts and Bogert's The Law of Trusts and Trustees. Also useful are the Restatement of the Law 2d: Trusts and a Restatement of the Law 3rd: Trusts that focuses on the Prudent Investor Rule.
The Scott treaties is on Lexis (ESTATE;SCOTT). The Bogert is on Westlaw (BOGERT).