Weekly trips to the library became part of our routine. Sometimes we would just look in the "topics" section and take home whatever books looked good. Some books had great photos, beautiful artwork, or interesting facts about a subject we didn't know about. Suddenly, we didn't miss the TV anymore. In fact, when we got a new one (almost a year later), I was reluctant. We now watch very little, while the habit of reading good books has lasted.
Suggesting to your son that "reading is good" just isn't enough. Does he have high-quality, age-appropriate books by well-known authors? Are his books about subjects he finds interesting? Do you read aloud to him regularly? Does he see you reading books either for pleasure or knowledge? Do you spend a lot of time watching TV? Your answers to these questions will determine how your son's reading habits develop.
Lastly, don't be afraid to turn off the TV! Limit time on the computer to half an hour. Get him his own library card, and go there with him regularly. Help him choose good books, or ask the librarian for help. Read a book that has been made into a movie, then rent the video. Discuss how they differ. (The book is always better!) Get him a subscription to a good magazine -- the library has lots of samples of kids magazines. Don't force the reading issue or he will rebel. Start slowly, then gradually make changes. He'll thank you later!