M&Ms and Zazzle's viral has a built-in ecommerce component. After you M&M-ize yourself you can add your character to a number of customizable products from Zazzle, including t-shirts, mugs, postcards, neckties, baseball hats and even postage stamps.
After you create your character, you can move to the "MPorium" where you can choose a product to personalize.
The customer is notified that they will be taken to a third party site (Zazzle) to complete orders.
Examples from Zazzle:
The advantages of this campaign over the elves is it can run all year long, and there is an immediate opportunity for an ecommerce transaction. The site offers truly unique gift ideas, and a way for users to capture their memory in physical form. The downside is that the microsite is very Web 2.0 and isn't likely to appeal to the over 55 crowd.