Before I started doing GTD I had been looking at various memory techniques. But what made me happy when I started doing GTD was that I didn't need to remember. In fact, some of the impetus to write something down comes from knowing that I won't remember. However, there has been the side effect that writing things down actually helps me to remember. And then there is this:

http://wired.com/news/culture/0,70399-0.html?tw=wn_index_4

I remember a discussion in GTDland about using interstitial time (in the grocery line, et cetera) to memorize things like poems, but I haven't thought about doing that in a while, much less trying to improve my memory. I really like the idea of memorizing the order of a deck of cards. And I'm familiar with the idea of associating each number from 1 to 100 with a color/thing, but I haven't been able to get that down. Maybe I should take another look at this:

http://www.vlaardingen.net/~tom/Mainmenu.htm