One thing I really love about banners is that it gets your site name and colors/logo in front of people while they are surfing the web.
There is nothing like a quick reminder about your program or site to make people return.
That is branding and that is on top of people actually clicking on the banners to come to your site. You can actually get some great results from banner clicks and that is because someone liked what they saw and decided to click for more information, Its a bit like a pre sell.
Anyway due to a increased popularity at my sites because I have set up a few cross promotions etc,