Free Affiliate Programs to Generate Revenue on Your Website

Biggest and best

These are the giants in the affiliate sales for websites arena.  They're all reliable.

• Amazon.com (Adsense and Amazon Web Services)
• Commission Junction - The most popular affiliate program.
• LinkShare
• ClickBank - Both an affiliate program and enables you to set up merchant accounts to handle credit card processing

Second Tier

• Affiliate Fuel - claims to have excellent tracking and payment
• Click2Lead - an affiliate program. Categories include automotive, books, business, clothing, family, food, games, and shopping.
• Free Turn-key reseller websites - Provides turnkey reseller web sites for domain names, web hosting and internet services.
• Online Direct Marketing 
• Refer-it - Pay-per-click search engine
• Share Sale - popular for merchants selling products and affiliate revenue

Other related tools

Banner exchange and banner generators

• Click4Click - free banner exchange program helps you increase traffic to your site.
   
• ABC Banners - free custom banners. Generate a banner from 20 templates with your own message.
• The Banner Generator - Another banner generator
• WebSiteGoodies Ad Rotator - free service that lets you rotate an unlimited number of banners of any size on your site. Click on the "Tools".
• WebSite Designs Banner Exchange -
• CyberGate Banner Exchange -
• Websponsors.com - Web ad network.

Reciprocal Links programs

• Link-Me - Reciprocal links program.

Informational

• PPC-Forums - informative resource for publishers and advertisers.
   
• The Net One - A directory to build traffic on your site.