There are over 75 pages of puzzles and problems to be found on Math Lair:
And, of course, there are answer pages:
And some hints:
To build your skills in solving puzzles and problems, you may also be interested in reading about problem solving, heuristics, and lateral thinking.
There are also several mathematics- and logic-related games on our sister site, All Fun and Games. Check out the Number Puzzles and Games, the Sudoku section, and the Brain Workout Puzzles.