LinkExchange (bCentral) - Offers 2:1 exchange ratio (for every two banner ads you display, your banner ad is displayed once). Owned by Microsoft, this is the largest banner exchange.
SmartClicks - Offers 2:1 exchange ratio, targeting options and comprehensive statistics.
Free Banner Exchange Megalist - Definitive source for information on over 350 free banner exchanges. Search based on criteria such as targeting options, content focus and credit ratios.
BannerTips - Offers very informative, hard-to-find insights and tips on every aspect of banner advertising, from design tips to a unique analysis of what impacts banner clickthrough rates.
Eboz - Comprehensive source for information on website design, marketing and e-commerce. Features original articles covering a vast array of topics of interest to all website owners.
SelfPromotion.com - Free search engine registration and links to other useful web promotion tools.
CNet's Builder.com - Primer on how to add images/banners to your pages, and much more.
WebMonkey - Walks you through the steps needed to display and align an image on your page.
Hits4Me.com - Well-rounded resource specializing in free tools for webmasters. Find information on all aspects of website operation, including expanding and enhancing site content, e-commerce issues, and marketing.