From NecroCosm Software:
AIM Ad Remover is a patch for AOL Instant Messanger (Version 4.1.x and above) that will remove the ads permanently from the AIM program. This makes AIM faster since it does not need to show the ads or download new ones every 5 - 15 minutes. Also, it prevents accidental clicking of the ads, which opens up an annoying web browser. This patch only needs to be executed once, and it is extremely useful and simple to operate.
Updated in this version is the ability to not only remove the ads from AIM forever, but also the tickers and the Instant Alerts. Other fixes and small changes have also been made.
Download here