I hate to endorse one product over another since there are so many cool computer games for teaching math facts. I'm sure there will be one your little guy likes. Some are slow, some are fast, some are sweet, and some have explosions. There's something for everyone, and it seems like there's hundreds of them on the internet.
When we got really serious with DS who has difficulty memorizing due to his LDs, we did Timez attack because it is timed and demanding. It's free (as long as you don't buy the upgrade which is just more graphics, not different content). We have had good success with that.