Help me use my brain.

[MrTrik]

Some ideas:

Learn to play guitar or some other instrument
Get a decent flight sim and learn to fly
Take up chess (though boring, really stimulates the brain)
Get a gun and hit the shooting range, compete at some point
Expand your reading list -- try new stuff
Equip yourself with S/W and H/W to mix your own music

Did all of these, still do most of them.