There are several companies that have highly effective affiliate programs. Here are a few examples:

1. Amazon Associates: Amazon is one of the most popular affiliate programs due to its wide range of products and high conversion rates. Affiliates can earn up to 10% in advertising fees for promoting Amazon products. The program provides various tools and reports to help affiliates track their earnings and optimize their campaigns.

Reference: Amazon Associates - https://affiliate-program.amazon.com/

2. Shopify Affiliate Program: Shopify is a leading e-commerce platform that allows individuals to create their own online stores. Their affiliate program offers a generous commission of up to $2,000 per referral. Affiliates gain access to a range of marketing materials, tracking tools, and dedicated support to maximize their earnings.

Reference: Shopify Affiliate Program - https://www.shopify.com/affiliates

3. ClickBank: ClickBank is a popular affiliate marketplace that connects product creators with affiliates. It offers a wide range of digital products across various niches, allowing affiliates to earn high commissions. ClickBank provides detailed analytics, conversion tracking, and customizable affiliate links to help affiliates optimize their campaigns.

Reference: ClickBank - https://www.clickbank.com/

4. eBay Partner Network: eBay's affiliate program allows affiliates to earn commissions by promoting eBay products. Affiliates can earn up to 70% of eBay's revenue share, depending on the category of the product. The program provides access to various tools and resources to help affiliates track their performance and optimize their campaigns.

Reference: eBay Partner Network - https://partnernetwork.ebay.com/

5. Commission Junction (CJ Affiliate): CJ Affiliate is a popular affiliate network that connects affiliates with a wide range of advertisers. It offers a user-friendly platform with advanced reporting and tracking capabilities. CJ Affiliate provides access to thousands of affiliate programs across different industries, making it a versatile option for affiliates.

Reference: CJ Affiliate - https://www.cj.com/

These are just a few examples of companies with effective affiliate programs. It's important to research and choose a program that aligns with your niche and target audience to maximize your earnings potential.