Not that I've been thinking about this allllll afternoon at the slight expense of doing actual work but...
I proudly present my five. Yup; 5. All with reasons. Not at all a rule breaker here.
The Hunger Games - I know it's a kids' book, but I think everyone should read it; it's a damning picture of the extremes of governmental control, reality television and the resilience of youth. I love it, despite how ruined I felt by the end of the trilogy. (and yes, I'm cheating because it's actually 3 books, but I am imagining somehow, somewhere there's a single book version of the set...)
Pride and Prejudice - Well, it was very close between this and Persuasion, but I think Elizabeth Bennet is just that little bit stronger a lead character. But yeah - it should be read because it shows a good case against stubbornmindedness, and because it felt right to balance a future dystopia with a classic tale of the past.
Harry Potter - Another childrens' series, I'm severely pushing at the rules set forth. But anyway, my reasoning for this one is that, as a young adult I read these books and my imagination ran wild. The world Rowling has created is so full of details and possibility and I think is in part to blame for my not-so-secret desire to be a writer. Also, because of the way Harry ages as we read, and changes before our very eyes from an innocent young 11 year old through his angsty teens, to the final 17 year old world-saving young man.
The Year of the Flood - although I think is the middle of 3 Margaret Attwood books, so can I have another imagined compendium with Oryx and Crake, The Year of the Flood, and then probably MaddAddam when I've read it. Because they're a more grown up Hunger Games; and worse they're a little bit more believable.
And finally... of the books of the world that I think MUST be read...
Deerskin - it's a fairytale retelling by Robin McKinley, and actually I don't think it must be read by anyone. But it's a book I read at least once a year and for some reason I just love it to pieces, so it's on my list out of loyalty and favouritism. So there.