@s804 I'd recommend Terry Pratchett books, and more specifically Guards! Guards!.
If you're more into hard fantasy, Brandon Sanderson wrote very enjoyable books, you should check his Mistborn book (which expands in to a trilogy).
If you want some easy to read SF, Asimov's Foundation is still a blast, and so is Ender's Game by Orson Scott Card. Plus they can be read as one shots, but they have sequels in case you enjoyed them enough.
Excellent suggestions, Guards! Guards! was what finally let me break into the Pratchett universe too, such a good and fun book to read. Mistborn series is one of my favorites, easy and pleasant to read but with a wild and engaging fantasy story.
I'd maybe recommend the Robot series before Foundation for SF fans, they are generally shorter stories and easier to follow. Foundation was pretty hard for me to follow and truly enjoy due to its weird no-protagonist structure.
Ah ah, I read Pratchett in the publication order and loved it, but after about two decades recommending it to everyone I know it's way easier to get people in by starting with the Nightwatch cycle. :D
Yes, the Robots short stories are indeed a nice addition, and probably easier to get into than Foundation! I did not enjoy the Robots full-fledged novels as much, though.
Still in SF, and keeping with the short stories idea, I'd also recommend The Martian Chronicles by Ray Bradbury.
Mistborn second series just wrapped up recently. Eagerly awaiting the third series so we can get on with Stormlight part 2 (where the two series merges into one. there is only one book left in Stormlight part 1, and release is expected next year i think).