I think banners get sub-conceously ignored by the brain for many reasons. It could be that they are a standard size that the brain associates with an advertisement or maybe its too busy with text and action and the brain blocks it out because it recognizes it as an advertisement. I think the best banners are the ones that sneak by the brains advertisement ignore auto-function. If the brain doesnt sub-conceously recognize it as a banner ad it doesnt ignore it.
Odd sized banners, banners without too much text or too much action, that kind of thing can make your banner slip by the brains auto-ignore. Then you just have to get the surfer to click it once they notice it, even though they know its an ad. I make alot of my own banners and I try to use the hottest babe I can find and the best pussy, tits, fucking sex, ass, thighs, legs etc pic I can find as the image, with just a bit of text saying the site name and 1 single sales text line with a call to action. I try to keep the banners as clean as possible to let the background image show through but not too much so it looks like a blind link.
Seems to work pretty well for getting clicks, getting sales is another story
I get alot of clicks to my sponsor, still working on the turning them into sales thing though