How much you earn is depending on the commission structures of the corresponding Affiliate Programs. You can involved in multiple Affiliate Programs as long as you can satisfied the Terms and Condition required.
Following are the list of the more popular Affiliate Programs:
1. Amazon (Recommended) : One of the largest self-administered affiliate program. Because Amazon is an established and trusted brand. This make it one of the most popular affiliate program to be involved in (click on the pic below and select "Join Associates" link at the bottom to register).
2. Clickbank (Recommended) : An affiliate program that focus on promoting digital products. If you have digital products like eBooks to promote and looking for a platform to affiliate your products, this is the platform for you. CLICK HERE to join Clickbank as vendor!
3. Commission Junction : Another popular affiliate programs that contain lots of products/services to choose from for your niche.
4. Linkshare (Recommended) : Yet another popular affiliate programs that contain lots of products/services to choose from for your niche. Click on the pic below to start your free registration.