the 728x90 you have in the bottom, I'd place it in the top of the page, between the blog's title and the first post, to have better CTR. And I'd replace the search box with a 300x250 or a 250x250 text/image ad.
the 160x600 in the ( right bottom) change it to 728x90 and put it in the top of the page. i think the ads text are better than the images.