C.M.
If the cyber school is free, then by all means go for it!
On the other hand, kids learn best through play and not through directed learning. Kids may learn tons of stuff at certain preschools that drill letters, numbers, etc, but if they aren't mentally ready for it then they will only memorize it not learn it. I think the biggest point of preschools is to learn socialization, how to sit patiently, wait your turn,and so on. Kids start kindergarten at all levels....some don't know their letters and some can read short books.
I think what they would really like to see from him when he starts kindergarten is that he can dress himself (button, snap, zip), write his name (preferably 1st letter capital and the rest lowercase), gets a full nights rest and eats a good healthy breakfast. Do this and he will be fine.
My daughter goes to a play based preschool and I'll admit that sometimes it drives me a little nuts. However, the kids that are ready to learn pick up on the information and some kids need a little more time to grow. My daughter is a quick learner, but I also supplement at home.
I don't use Hooked on Phonics because it is pricey for the whole set and I don't need DVDs. I got the level 1 phonics workbook by Teacher Created Resources and I love it. After he learns his letters a good set of books is Animal Antics by Nora Gaydos. My daughter loves reading those. For math, we use giant foam dice, both with dots and numbers, use them to either recognize the numbers or do simple addition and then practice writing the numbers.
Good luck! I'm sure your son will do just fine next year. My daughter will be starting kindergarten also, so I'm excited but nervous and sad.