- They have a cool Alcumus (free) bot.
- The forums can be a tad intimidating, however.
- Excellent collection of competition problems. Not that many have solutions.
The Art and Craft of Problem Solving: Rich collection of problem-solving principles followed with examples, problems
(A harder book: Orange problem-solving book. Yeah, it’s much harder.)
Coffee and Matrix Algebra
Love and Maths: Inspiring but can get a bit technical / confusing.
The Music of the Primes
1089: Short and fun. Easy to start with!
A Mathematician’s Apology
Documentaries / Movies:
LMS Popular Lecture Series (Youtube). I recommend Prof. Takashi Tokieda’s Toy Models talk. His site is also really cute. :3