R.D.
Do you mean regular manufacturer coupons? Or store specific coupons? If you want manufacturer coupons, here are some places to start:
www.smartsource.com
www.redplum.com
www.coupons.com
www.allyou.com (http://bit.ly/fUBnkp)
www.target.com (http://bit.ly/e0jkUF)
http://couponsdealsandmore.com/printable-coupons/
In order to print coupons, you will have to download the coupon printer. (After selecting the coupons you want, click "Print" and the first time it will prompt you to download the application. Just click "Allow" or "Run" or whatever it says. Easy-Peasy.)
The best thing to do is call around the stores in your area to find out if they double, and to what amount they do. (Some double to $.50, some to $.99 - it just depends.)