Whether you're into jigsaws or riddles, a good puzzle can exercise your brain and leave you pondering the universe. Consider taking up puzzling as a hobby and open a world of fun. The library and the internet have loads of resources for brain teasers, logic puzzles, pattern-matching, cryptology puzzles, sudoku, crossword puzzles and more.
101 Puzzles in Thought and Logic by 
Intriguing Lateral Thinking Puzzles by 