Problems learning to memorize multiplication are a real red flag for dyslexia, I'm sorry to say. This interesting page tells you many dyslexia symptoms: http://www.dyslexiavictoriaonline.com/inofdy.html

My son still works on this and we have used everything. I just found these books, though, which sound pretty good:
http://www.amazon.com/Ice-Cream-Spi..._1?ie=UTF8&qid=1334291454&sr=8-1

Also, you can find story-based flashcards on Amazon. Each multiplication "sentence" is made into a picture, which is easier for some kids to memorize. It also helps to figure out how he learns. If he's an auditory learner, perhaps songs?