I have been preparing for mathematical olympiad since last year and I have read many books.
Which are like as follow:
1.Problem Primer for mathematical olympiad.
2.Problems in mathematics (By V.Govorov and fellows)
3.Challenge and Thrill of Pre-collage mathematics (In association with NBHM of INDIA) and many more books, but no book amazed me. Yeah I believe that problems were tough enough to send me in coma sometimes but still I can't enjoy mathematics with them.
I want you guys to suggest me some adventurous Mathematics books which gave me a pleasure which I got by reading Young and Freedman, Resnick, Halliday and Walker, IE Irodov in physics.
This year I got chance to participate in International Olympiad Metropolis held in Russia (I thoought it is good to mention here so that you will not provide high school mathematical content in your answer). Hope you guys got it. Any suggestion is heartily welcome
These are my favorite ones and I hope you will like them:
$1$. An excursion in mathematics by Bhaskaracharya Pratishthana.
$2$. Putnam and Beyond by Titu Andresssu and Raven Gelca.
$3$. This link provide some other good books