The Hitchhiker's Guide to the Galaxy

Don't panic.
Only rarely does any media manage to merge sci-fi with humour - for most other genres, they can meet sci-fi somewhere in between, but it isn't easy to meld comedy, from my experience.
H2G2 towers above the rest when it comes to this - through a spectacular mixture of humour in the vein of Monty Python, surrealism/absurdism and excellent quotes.
There's little to no plot, considering the novel takes its hitchhiking aspects seriously - so the book is just characters meeting, interacting and then moving on. This lack of story can understandably be a dealbreaker to many (the destruction of Earth takes place within the first few chapters, and it's just glossed over). But if you can read beyond that, H2G2 begins to take a life of its own. Another plot point I loved was the treatment of sentience - and the iconic ‘the answer to the ultimate question of life, the universe and everything.'
All in all, as an intro to the series, I couldn't have asked for anything better - and even read as a standalone piece, the humour is amazing - well worth reading for, and I'm looking forward to reading the entire series soon.