I'm wondering what would be the best ad placement for a blog with this setup? I think I have it pretty good now, but ad placement has never been my strong point. http://forgottenknowledge.net/
I would remove the 468 banner on top and replace it with 2 square ads side by side. The biggest ads you can put in there. Keep them the same size though. 2- 336 wide ads or 2 - 300 wide ads.
I have performed different google adsense placement experiments, Please see following link, It might help: http://techbrij.com/576/google-adsense-tips-placement-experiments