Basic Logic Primer. But along with the primer we have a number of suggested followup resources. One new resource to add to the list of tools is The Logic Classroom. The Logic Classroom is a course in basic logic. Each study has review questions, exercises, and answers to the exercises. It's layout and design is simple, but the content is great. This resource provided by Dr. Elihu Carranza, author of Logic Primer.
Check out The Logic Classroom here.