I'm increasingly liking Ebates.
Here are some major stores / brands that have decent rebates from Ebates:
4% at Target
4% at Sears
4% at JCPenny
5% at Home Depot
8% from Starbucks Stores
6% at Petco
To find other online vendors that have offers from Ebates go to the site and click on the 'Stores' tab. Or you can just use their search box to find a specific store name.
These discounts only apply to online purchases and you have to go through Ebates to get them. But if you would have bought something through one of these sites otherwise then why not save yourself an extra 4-8%?!
For more on Ebates see my previous article on them.