I'm not going to spend too much time on this. At some point, especially if you're running an e-commerce site, you may be interested in trying a service like Groupon—a crowdsourcing service that provides deep discounts on a product or service you provide, if a preset number of other people purchase the coupon.
Personally, I don't have any direct experience with using Groupon, but I haven't heard good things. From what I understand, however, the deep discounts, plus the fee that Groupon charges, can potentially lead to pretty severe losses on the items sold. The underlying philosophy is that these losses are okay because they introduce your company to new customers, who could potentially come back another time to make future purchases. The problem is that—again, from what I understand—it rarely works like that. The people who buy Groupons are people who only want the discounts, and the repeat purchases don't usually materialize. So think carefully about whether you want to go this route for marketing.