Six weights
A nice variation of the classic balance scale weighing puzzle. First saw this in PProblem SSSolving.
Puzzle
You have six weights. One pair is red, one pair is white, one pair is blue. In each pair, one weight is a trifle heavier than the other, but otherwise appears to be exactly like its mate. The three heavier weights (one of each color) all weight the same. This is also true of the three lighter weights. In two separate weighings on a balance scale, how can you identify which is the heavier weight of each pair?