A friend of ours with a milk allergy made an interesting discovery the other day: rice cheese. Better yet, Vegan rice cheese. This "cheese", made by Galaxy Nutritional Foods, comes in slices like the Kraft Singles. I tried them myself and while they weren't bad, I wasn't that excited about them. It seemed more like a really soft cracker than cheese, but it would probably be alright on a sandwich or something.
The good thing is that my son really liked it. He felt so special to be able to eat cheese like his sister. He kept asking for the "cheese that doesn't make me sick". It warmed my heart to have him feel like he was included in something that the average person participates him. That alone made it worth it!