Here at 99Tangents, we’re very fond of brain fitness. And The Ririan Project has a great list of ways to keep your brain fit and healthy:

Just stop
Hit the streets
Mix it up
Read a book
One-cup-manship
Engage in a debate
Grab the Brainbox 360 controller
Subscribe to a daily newsletter
Curry favours
Grab a cue and play pool
Learn an instrument
Being boron
Fresh air golf [...]