WebAdverts
Maintains a set of rotating banner ads or for setting up a banner exchange. View the South Park Link Swap and download a version of the script.
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Advertise
Perlscript allows for simple banner rotations. Two forms include one on the server-side while the other CGI script reads HTML. Get the freeware.

BannerMan
Banner management script works using either Server-Side Includes or Image tags. Look at the demonstration and view the help file.

Ad Rotator
Displays a random banner ad with a matching URL. Contains an interface that allows users to add and remove banners. Demo and download.

AdRotator.com
Presents a completely free banner rotation system. Check out the demo and become a member.

Bannermatic Ad Rotator
Script will operate a rotating banner ad system. Comes in three different flavors and includes a manager script called Banman.

AdDesigner.com
FREE banner ads for your website in seconds! Choose from over 70 unique, fully-animated designs, customized with the text and fonts you want. Perfect for using with banner exchanges or for other ad campaigns.

Free-Banners                                                                                                                Drive INSANE Traffic To Your WebSite! Free Banners is a fantastic new way to get more exposure for your web site while earning you CASH! Just think - when you become a member you can get your banner ad displayed on other members sites. Even better.

Animation Online Free Banners
Use Animation Online to instantly create free animated banners for advertising on the web using templates. You do not need to be an animator or an artist!

Amazing Instant Online Animated Banner Maker
MediaBuilder's free online animated banner maker allows you to create your own custom animated banners in minutes!

BannerCreator.nu
Create a banner for your site online for free at this site and and have it emailed to you or upload it directly to your server.

Quickbanner
Quickbanner is a free online banner creation tool that allows you to create high quality GIF banners in a matter of seconds! Many banner styles to choose from.

The Animation Station - Free Banners
They currently have over 600 free banner templates to choose from! If you need some templates or maybe just some ideas, you'll want to stop by this great site.