I love to play Sudoku. In this game, you need to enter the numbers 1-9 into each empty space. Each row, each column, and each 3x3 square can only contain one of each number. It's fun, addictive and you don't need to be good at math (which I like!)
Here's one I just discovered yesterday - it's called Futoshiki, or "Son of Sudoku." Every row and column must contain the numbers 1-4 (or 1-5 as I've seen in some cases) and again they can only contain each number once. The puzzle also has "greater-than" and "less-than" symbols that you must obey. This one is really hard!
Crossword puzzles can be rewarding, but I'm no good at them so I never bother to fill them in. However, I found a website that lets you create your own, so now I can have fun with them too. Go here to start creating. Also, if you haven't seen the movie Wordplay you totally should. It's fascinating!
What are some of your favorite games or puzzles for a rainy day?