Check out www.starfall.com.
My 2 yr old and 4 yr old love it!
You can also do a Google image search for alphabet coloring pages and print all sorts of things for him to color.
The Leap Frog fridge letters have been great too.
There are tons of DVDs out there too. Sesame street shows are always a winner.
He may be more interested in literacy "on the go" rather than sitting still for workbooks and flashcards. Try to get him to notice the big "K" on Kroger, point out S-T-O-P at every stop sign, etc (we have taken walks in the evening where we make the stop sign on the corner our destination, then my husband picks the kids up high so they can touch the letters).
When you point out a letter, be sure to say it's sound. Boys seem to like the sounds more than anything!
A trip to the grocery store is a literacy experience too (so says a friend who teaches first grade). Let him help get the groceries off the shelves and put them in the basket, and point out words and letters on boxes and jars in the process. For example, help him notice that you're getting Jif peanut butter with a "J" instead of Peter Pan with a "P". Anything that includes the letters of his name is even better.
I believe Earth's Best and maybe even Newman's Own makes organic alphabet cookies for kids.
Point out the letters and words on things in his world at home too. Show him the "A" on the apple juice jug, etc. You can also get a sharpie and address labels to label storage bins and things in his room. Put sticky notes all over the house...
If you have sidewalk chalk, draw his name on the back porch, then ask him what other things he'd like you to write. If you have a sand box, you can trace the first letter of his name in the sand.
Go to a teacher supply store and get an alphabet border or poster to put up in his room or in your play room. We found a cute alphabet bear poster at www.art.com that my daughter loved.
He'll pick it up when he's ready. It's probably just not important to him right now.