I am so amazed at how impressive our brains are and how we are always forming new synaptic connections. It actually hurts my brain to think about everything that is going on up there! The most effective way to keep your brain fit is to constantly test your knowledge and keep your mind curious. Cross work puzzles, reading books, and learning new things are great ways to maintain brain health.
My favorite brain training websites (I have subscriptions to both) are:
The Brain That Changes Itself By Norman Doidge I was so inspired by this book that I traveled to meet some of the featured doctors. Excellent read!