A while ago I worked on a project where we had a single client that had multiple products.  Each product required its own product site including a shopping site for the products.  Upon discussing the options with the client, who was not fond of the idea of having to track and maintain a multitude of different websites AND their associated shopping portions, an idea was proposed to take the concept of a hybrid Bridge-Facade Design Pattern and modify it somewhat to create a single shopping engine that would appear congruent with the product site, be a single location for inventory tracking/ordering, and provide a single access point that could be reused as the client added new products to their portfolio.

In English, the client wanted to keep their websites for each product seperate from their ordering/shopping system, but wanted the shopping system to change its visual appearance each time it was accessed to resemble the referring product site.

So after some pretty interesting concept meetings, we proposed using a modified "Facade" pattern on top of our shopping engine, creating themes that would be applied at runtime based upon an algorithm and analysis of the referring site... oh yeah, at it had to appear SEAMLESS.  Each of the product sites were unsecured, yet the shopping site was SSL.

The following diagram illustrates the concept:

The solution was quite ingenious.  Inside our .Net application for the shopping engine, we used a couple of techniques and algorithms to determine the appropriate presentation and then applied that presentation based on the particular shopping engine the user expected to see. Kinda neat huh?  I can't disclose exactly how this was done, but suffice to say, it was quite tricky.  Once in place, however, the engine was able to load the appropriate products, and track the member's order correctly... and interestingly, the process was optimized and occurred amazingly fast.

For this particular client the solution was perfect! Not only would products and transactions be handled through a secure layer, but we could (by reusing our styling from the product site itself) completely remove any development time involved with recreating the shopping experience across products. Just keep in mind, that with proper planning, anything you can imagine can be created.