Reading.  I believe reading is the most enriching frugal activity one can engage in.  It forces you to use your brain (unlike the TV), opens you to new ideas, helps you learn and grow, and is relatively inexpensive.

I read newspapers, magazines, books, and the internet.  I usually read to learn something new-- lately, car repair, cooking, and wood heat.  I love to learn and add to my skill set.

We encourage the kids to read and take them to library from time to time (See my post, How to Use the Value of Your Local Library).

What are you reading?