Banex is a nice PHP/MySQL banner exchange program with anti-cheat functions, admin panel, ratios and more. Version 2 includes huge improvements to the administration panel and layout, and also adds multi-banners per user support. Mods available.

While not exactly a banner exchange script, AutoPub allows one visitor at a time to add his/her link with a little banner on your page which will remain until the next visitor replaces it with his/her submission. Configurable parameters include: delay time, color, fonts, banner's width and height. Also features: a gallery page to show all the old banners, a complete automatic installation and a password protected admin panel. 2.1a: added a little anti-hackers protection.