I started a coupon train- we have a group of 5 people who send coupons to each other. I get my coupons, initially, from the newspaper, packages, magazines, and I send e-mails to companies when they are offering them, or to ask them for coupons. I also send genuine compliments & complaints to companies, which often result in very good coupons.
That said, I am very careful about how I use coupons. I only use them for things I either buy anyway, or want to try and would have bought eventually, even if I had to pay full price. (Or, of course, when I get ones for a free item.)