The Hitch hikers Guide to the Galaxy books are brilliant.
Much like Terry Pratchett and his Discworld series, these books are slighty wierd but superbly writtten. Not only are the books very funny but also intelligent and he links together some great ideas on life, the universe and everything as he goes along.
The main character Arthur Dent is removed from Earth by his friend Ford Prefect just as it is about to be demolished by the Vogons. Among other things, he is advised to take a towel....very important!
The books follow his time travelling in space and on various new worlds meeting some interesting characters along the way.
If you are a fan of Pratchett, Douglas Adams humour will suit you perfectly. With ideas like - "the secret to flying is just to forget that you are falling", simple really.
Although the brilliant humour is there throughout the 5 books, there are periods where it slows down a bit. Douglas Adams had many disputes throughout his professional life and sadly it affected some of his writing but overall these are brilliant, funny books and without doubt up there with my favourites.
Once completing the books, its worth seeing the original tv series from the 80s, very basic like the original Doctor Who series but lots of fun.