You don't have to give milk--there are lots of foods out there that offer the calcium, protein and fat that kids get from dairy products. Talk to your pediatrician about coming up with a list of foods that can help replace it.
Soy, almond & rice are all good if he wants milk w/ his cereal, and they do offer nutrition as well, but it is not really a 100% replacement for the nutrients in cows or goats milk. They are yummy & nutritious in their rights, but do keep in mind that a lot of the soy/almond/rice milks tend to be high in sugar, much more so than dairy, so read the labels carefully.
Also, depending on his reaction, you can try Lactaid, which is milk that has had the lactose broken down; there is a difference between a true milk allergy and a lactose intolerance, and most people who think they are allergic to milk are actually lactose intolerant instead. Cheese is sometimes "safe" for those with lactose intolerance because the culture used to make the cheese breaks down all or most of the lactose in the process of making the cheese.