Blend the ads into the content. People are suffering from banner blindness, so they won’t click the ads if they look like ads. Place the ads in the middle of the page. Let the color match the other links in yor website. If the link looks like a title, it will get more click throughs. Do not have any borders. Put ads before the content, in the middle and at the end of the content. People will click a relavent ad after they finish reading the content. AdSense search box can be put in 404 pages. You will get more 404 visits than you think!