Redirect purchase at item level to another site
Sometimes you have items that you want in your store, but you can't (or don't) resell them. If that button can take the customer to the third-party site's page of your product.
For example: Kindle files, iTune files, mobile apps, etc. need to be purchased on another company's site, but if you are the producer of said book, music files, mobile app, you want it included seamlessly in your own shop.
This would also be good for affiliate links.
Please see our “Product Retailers” extension here: http://www.woothemes.com/products/product-retailers/