This paper describes anti-unification algorithms for computing least general generalizations of two expressions in a functional programming language with recursive let. First, by exploring a semantic approach to the problem, we argue for an improvement of the technique used in previous papers which avoids infinite chains of less general generalizations. Second, we present a (non-deterministic) nominal general anti-unification algorithm applicable to general expressions, which is complete, terminating and requires polynomial time. Third, we propose a specialized anti-unification algorithm applicable to two or more garbage-free ground expressions that produces a single least general generalization in polynomial time, and which can also exploit further semantically correct equivalences. Our results have potential applications in finding clones in functional programs.