If you like Sudoku and can do basic math, you will be challenged by KenKen.
I love these puzzles- they are more challenging than Sudoku and very addicting.
You can learn more about them at the KenKen site- there is a tutorial video that is the next best thing to having me beside you as a tutor.
Start with the 4x4 puzzle and work your way up to the 9x9.
I am so addicted, I do a 9x9 every day!
It's a great way to brush up on your math and keep your brain flexible!