Affiliate Programs for your Niche Website

Find affiliate programs for your Niche website by doing a search on the following sites:

Associate Programs
Refer-It (over 6,500 programs)
Affiliate First
Clickbank

With Clickbank, you can also use a tool called Affiliates Alert.
It searches through the Clickbank database and returns the affiliate programs related to your keyword, it also lets you know when new ones enter the market.
You have to have a paid version of the tool to access the clickbank link, but it does allow you to visit the website - so you can visit the website and get the clickbank code, or now that you know what category it's in, you can head over to the clickbank marketplace and browse the category so you don't have to pay for the program (although it's a time-saving tool if you do).