This page gives possible rectangles for those polyominoes with numerous primes. The possible rectangles for ones with few primes are generally easy to deduce.
In each table the number in the left hand column is one side of a rectangle and the numbers in that row (or sometimes rows) show the second side. A red number in the left hand column indicates that the set is rectangles is (or may be) incomplete. An 'all' in the last column indicates that all numbers after the last in the row are possible.