The Andy Warhol Museum is not large, but it is well worth the trip. Sometimes they will have another artist as well, but go for all of the Warhol's. They have the best collection. Mr. Warhol was born in PA, so it is the perfect location for his museum.
You will see some of his finest work and they also preview movies/films of his and they tend to run all day. Don't worry about coming into the middle of one, as they don't have a story line (I am clearly not bright enough to understand these films, but they are interesting).
If you hate Pop Art, you will be miserable. If you like Warhol though it is the best place to see his work.