Don't know how many readers are already well familiar with this?:
In 1999, the "Eternity" puzzle, a jigsaw puzzle on steroids, composed of 209 pieces shaped as equilateral triangles and half-triangles, was launched by Christopher Monckton, with a prize of one million pounds for the first person to solve it within 4 years. Naively, Monckton thought it would take at least that long to solve it (and even put up half the reward from his own funds). One of the early websites for the contest is here (where one of the pages gives the original rules; several other links are now dead):
Less than a year later though it was solved, and the prize awarded to 2 Cambridge mathematicians. You can read more about it from this 2001 plus.maths article:
With a little more study, Eternity 2 was launched in 2007, a 259-piece puzzle comprised this time of squares with colored edges that had to match up for the solution. It has better lived up to the hype, as the new $2 million award went unclaimed after Jan. 2011, the deadline for the prize -- and so far as I'm aware it remains unsolved!
AMS posted this blurb about the puzzles just last year:
I don't believe the puzzle is for sale any longer, other than second-hand copies.