If you're a fan of The Twits or any of his other books, this might be a fun site. (Don't panic--you can turn off the animation when they start to drive you crazy.)
Back in the 1980s, Dahl wrote a book about a man who saved the life of a king and was given the right to have sex with any woman in the kingdom. As incredibly un-PC as that is, I'd love to find a copy.
I'd nominate The Twits as his best (or most satisfying) book. According to a number of pages, Matilda was voted his most popular--not a bad book by any stretch but nowhere as funny and disgusting as The Twits.