I'm teaching PF (prime factorization) GCF (greatest common factor), and LCM (least common multiple). I haven't always taught them together, but the last few years I have. It is a lot of vocabulary for the kids to learn, review, and master, but I really feel it works well together.
I teach with something that I learned about 4 years ago- stacks, Danica McKellar talks about it in her book, Math Doesn't Suck.
Stacks are math done with an upside down division symbol, sometimes called upside down birthday cake, and anything else that someone names it. I don't know if it really has a specific name. I found this "Youtube Video" that calls the Indian Method. She makes a straight line where I would make an upside-down division symbol. In her video which does three numbers, which before today I had not seen and now I love it. Check the video out.
I love them! I teach students first by doing factor trees. What do you do? What is your favorite?