Haha I really enjoyed this. I concentrated on
3D Stereogram which allows you to draw a picture, press the generate button and then it does one of those 3D eye puzzle things. I found it really easy to get it to work on my laptop monitor (much better than on paper when I tried doing the in that book thing). It turns out I suck at drawing with a mouse but the below picture should say 'tas666'. Click on it to get the full picture (it doesn't work so easily small). You have to look through the picture...ie look at it unfocused and then slowly bring your eyes back into focus.

PS Bah, just realised that that's as big as the picture gets. Sorry!