Here’s an interesting project about staying mentally fit (I think “fit” is a better sense here than “healthy”, btw).

For the record, my five-a-day for keeping the engine running:

1: Read - blogs, books, fiction, non-fiction, work-related or not.
2: Play guitar - of course
3: Walk - open air, outside, whatever the weather. Clear the mind and get perspective
4: Solve something - a crossword, math or logic puzzle.
5: Write something