There is a wonderful program offered by ACE Ministries Called ABC's with Ace and Christy reading readiness program. This program combines songs for each letter and sound, workbooks, Parent's Manual, games, stories, Cd's, the works. I have used this program myself and it is phenomenal. My child was reading on a first grade level at age four and she loved every minute of it.
I would suggest trying a multi-sensory approach. Using all of the senses gives many options for the information to be processed by the brain. In addition to the sense of sight in association with each letter, use physical activities (ie:walk the lines of a giant letter A written on the driveway), the sense of taste (eat an apricot), the sense of touch ( use applesauce to fingerpaint the letter A), the sense of smell (smell an anchovy) etc.. Novelty will also help with the connections.
First, how old is your son? Are you teaching letter identification or writing of the letters? There is a definite developmental progression for learning and writing of the letters. For example, diagonal perception does not come in until between 4 1/2 and 5 years of age. That's why many letters such as A, K, M, N are hard to write for many pre k children. So make sure he is developmentally ready for learning the abc's by consulting books such as My Four Year Old by Illg and Ames or My Three Year Old by the same authors.
I would like to second the suggestions about LeapFrog DVDs and refrigerator magnets. If you are not opposed to having your child watch DVDs, these would be a good choice. "Letter Factory" introduces all the letters and their sounds (for the vowels, they just do short vowel sounds on this DVD, but later ones deal with long vowels, as well as blends, etc.). The letters are given personalities and catchy tunes. My kids both loved the DVD. They learned the sounds of letters very young and were able to retain the the information because of the supercatchy tunes.
LeapFrog also makes a "Fridge Phonics" alphabet set toy that plays the same tunes as on the DVD and provides a tactile interaction with the letters. But any letters children can hold and touch would work well (refrigerator magnets, wooden alphabet puzzles where the pieces are shaped like letters, etc.).
I'm not sure how appealing these would be if your child is older than maybe 4 or 5, but for younger children they are great.