Via Watershed Studio:

Now through August 31st, 2009 you can purchase OIOpublisher for just $39 (normally $47) by using coupon code “BLUE-WSHED” (no quotes).  If you’re unfamiliar with OIOpublisher, it is a PHP based ad platform with a focus on performance, control and ease of use. It allows you to easily serve advertising on your blog or website and keep 100% of the revenue you bring in.

[Update: August 2010 OIOpublisher Coupon Code - Now through August 31st, 2010 you can purchase OIOpublisher* for just $37 (normally $47) by using coupon code "SOLAR-WSHED" (no quotes).]