An obvious example might be a competition to design a new product, similar to Walkers recent efforts to get the public to define new flavours of crisps.
Possibly slightly less obvious would be to address a couple of issues most website managers would profess to having, search result relevancy and product hierarchy. So, how about having something similar to Googles new additions allowing your users to rank site search results
or comment? Or allowing users to re-categorise products? It would be an interesting experiment to see the affects on conversion rates. The theory being these would improve as the customers with common interests improve each others routes to find products.
