Highly recommend. There's a 6th Hitchhiker's book written by Eoin Colfer (And Another Thing) with the permission of Douglas Adams' family. It's alright and completes the series.

My favourite book, though, is Last Chance To See. He travels the world and writes about animals on the brink of extinction. After I read it, I hated mankind in general even more. Didn't know it'd be possible..

The Dirk Gently books and Starship Titanic are good fun as well.