There are many coupon resources out there on the web. If you are going to sign up to any of them, make sure you have a separate email account for all incoming messages. You might be surprised how much spam you'll get.
Here are a few sites I really enjoy and only receive legitimate coupons and information:
Right@Home - An S C Johnson company providing coupons for products such as Windex, Glade, Scrubbing Bubbles...etc.
VocalPoint - offers free samples, coupons, surveys about products in return they would like you to leave feedback regarding the product they sent you. I've received FREE Kashi cereal coupons, FREE Rice Krispies cereal coupons, FREE samples of Olay Pro-x and Secret Clinical Strength.
Betty Crocker - offers coupons and recipes related to General Mills products, also has an area where you can input what ingredients you have on hand to create a meal.
P&G Everyday Solutions - offers coupons and incentives for Proctor & Gamble products, and eSaver coupons you can load to your Kroger Plus Card
Marzetti - receive coupons and offers by signing up
Home Solutions News - offers coupons and tips for household products