Here is a site that updates puzzles regulalry:
 mathschallenge.net
  • Irrationality Of E 17/10/2010 01:00

    Prove that e is irrational.

    Problem ID: 377 (17 Oct 2010) / Difficulty: 4 star
  • Rectangle Construction 17/10/2010 01:00

    Find the connection between the constructed length and the original rectangle.

    Problem ID: 376 (17 Oct 2010) / Difficulty: 2 star
  • Inscribed Circle In Isosceles Triangle 16/08/2010 01:00

    Find the radius of the circle inscribed inside the isosceles triangle.

    Problem ID: 375 (16 Aug 2010) / Difficulty: 2 star
  • Multiplying Magic Square 16/08/2010 01:00

    Show how the values 1, 2, 4, 8, 16, 32, 64, 128, and 256 can be placed in a 3x3 square grid so that the product of each row, column, and diagonal gives the same value.

    Problem ID: 374 (16 Aug 2010) / Difficulty: 3 star
  • Polynomial Roots 07/08/2010 01:00

    Prove that the roots of the polynomial, xn + cn-1xn-1 + ... + c2x2 + c1x + c0 = 0, are irrational or integer.

    Problem ID: 373 (07 Aug 2010) / Difficulty: 3 star
  • Hops And Slides But Never Square 07/08/2010 01:00

    Prove that the minimum number of moves to completely reverse the positions of the coloured counters can never be square.

    Problem ID: 372 (07 Aug 2010) / Difficulty: 3 star
  • Irrationality Of Pi 24/12/2009

    Prove that π is irrational.

    Problem ID: 371 (24 Dec 2009) / Difficulty: 4 star
  • Square And Round Plugs 24/12/2009

    Which fits better... a round plug in a square hole or a square plug in a round hole?

    Problem ID: 370 (24 Dec 2009) / Difficulty: 2 star
  • Algebraic Cosine 30/11/2009

    Prove that cos(x) is algebraic if x is a rational multiple of Pi.

    Problem ID: 369 (30 Nov 2009) / Difficulty: 4 star
  • Inscribed Square 30/11/2009

    Find the side length of the square inscribed inside the right angled triangle.

    Problem ID: 368 (30 Nov 2009) / Difficulty: 2 star
  • Infinite Circles 15/11/2009

    What fraction of the large red circle do the infinite set of smaller circles represent?

    Problem ID: 367 (15 Nov 2009) / Difficulty: 4 star
 Scientific American - Math