Whenever I am shopping online, as soon as I see the field for entering coupon codes or promotional codes, I open up a web page and do a web search for "the name of the company coupon code" to see if I can find a deal. You can find percentage off coupon codes, free shipping codes, and more out there if you are lucky.
The Google approach is hit or miss, however, and can take up some time. Some of the sites are not easy to navigate, codes are expired, or they have the keyword in their page, but no actual code for the site you are looking for. I have found a site I can go to first - that is easy to navigate and doesn't waste your time. It's called Coupon Chief and it's at http://www.couponchief.com.
Coupon Chief also has an interesting feature where if you submit coupon codes to the site and people use them you can get a share of the sales. I assume this works when the shoppers click through the Coupon Chief site. They have an easy to use page for submitting codes as well. I get codes in the mail from retailers all the time, so I might try this feature. It's nice to share the information, even without making any money from it.