Originally Posted by Mike L
Myra Breckinridge would be a good first choice, as that's usually considered the best of his "social" novels.
If you prefer his historical fiction, I can recommend Lincoln. It's an account of Lincoln's life during the US Civil War, seen through the eyes of several of his contemporaries. I found it quite gripping.
I haven't read anything else by Vidal yet, but I've got Burr on my list.