I LOVE triangle flash cards! It's a great way for students to practice their facts and actually "see" fact families (related facts). Directions are included on how to use these cards. They are a great set for the classroom, as well as good practice at home.
Facts begin with 2+2 and sums go to 20, except for 10 - my tens go to 100 since counting by 10 is so important for students to master (and helps build the concept of 10). Other graphic versions are available in my store as well....please check them out!
You can also check out how I use these to build math fluency in the classroom at my blog: www.adventuresn2grade.blogspot.com