I have noticed that some reseller companies are advertising free credit for web advertising on Yahoo, google or MSN. I would like to look into offering this to my customers. Any links or suggestions on where to find more info?

Thanks.

You can buy coupons for less than their value at various forums, which you can then offer. Also, if you have enough customers, you could approach Google directly and they may sell you coupons directly - I have no idea what price you would be offered though.