You will be looking at places in West Virginia or Colorado typically. I cannot recommend any spots off the top of my head, but those seem like the two popular choices.
Thanks- I will google those areas and see what I can find. We can't wait really - I wish there was somewhere that we could go in the winter (Christmas vacation) where the water and air would still be warm.
I love West Virginia for white watter rafting. They have some of the most exciting and most well put together trips I have ever seen! It is defiantly something you want to try at least once.