I will have to get The Thought Gang immediately because this is the first time I've born witness to a fellow Barth fan. I read "Lost in the Funhouse" in a creative writing class and it changed everything I'd thought about writing. As for "Hotel New Hampshire", when that movie 'Hope Floats' came out, I actually got angry. I could only think, "It's SORROW floats. Not hope. Sorrow."
My all time favorite book ever is:
Les Liasons Dangereuses by Pierre Choderlos de Laclos
I don't care how many movie treatments of this book you've seen, it's worth reading and reading carefully.
Other favorites authors/books:
Literature:
William T. Vollmann - You Bright and Risen Angels
Arudhati Roy - The God of Small Things
Margret Atwood - The Blind Assassin
Cormac McCarthy - Border Trilogy (Though The Crossing made me briefly suicidal)
Raymond Carver - Anything. Just pick anything. It'll rock your inner world.
Sci-Fi:
Neil Stephenson
Horror:
Stephen King - but only his short stories. His books do nothing for me. His short stories put me in quite a state.