Where can I find more information on stamps and where is a good place to sell collectible stamps?

I’ve been charged with researching the value of a very large collection of vintage postage stamps, some of which have already been determined to be quite valuable (up to a few hundred dollars). Others are still a mystery. If I can accurately price the stamps in the collection and find a place to sell them, I will get a significant cut of the profit. Naturally, I want to figure out the value of as many of these stamps as possible, as accurately as possible, and I want to sell them somewhere where I can maximize my profits. Any ideas or suggestions?