Ugenie is a new comparison engine that has a unique feature (as far as I know):
Ugenie is a powerful new tool to help you find the best prices on books, music, movies, and video games. You can shop for a single item, or customize a bundle of items. Either way, we’ll compute the bottom-line price (including shipping, taxes, and discounts). We find the cheapest way to buy the exact items you want from one or more merchant sites.
You can find a really nice review of Ugenie at ReadWriteWeb.
For the moment, Ugenie is limited to cultural goods (books, music, movies and games). The user experience is quite efficient: a full-text search engine lets you search products (and not offers, so you may find products that are not available anymore), build your bundles and then compare prices. Your bundle could then be ordered in one or several merchants, as new or used items.
Some social stuff has been added – tags, ratings, integration with del.icio.us, digg, reddit – but they feel like gadgets for the moment.
I think Ugenie has found a good way to set the difference between them and the other shopping engines. I’m waiting to see how they will enter the electronics or computing categories, where shipping costs are higher than in cultural goods and the bundling practice is quite common.