I used to work in high-end retail. Dolce & Gabbana (as well as their cheaper line D&G) always generate knockoffs, particularly in sunglasses. Look into those. Bulgari is another brand those sunglasses always get knocked-off.
Chanel and Louis Vuitton are the two most popular purse knockoffs, with Chloe (yes, even in America) and Burberry. Fendi is easily knocked off because of it's (hideous) pattern, and Gucci (their Guccisima line) is always done.
Prada and Versace knockoffs are abundant but always really bad. There are replicas of the Hermes Birkin bag but they're all horribly done and very fake.
As for jewelry, Tiffany and Cartier are the two that come to mind, as well as Michele Watches.
I have no idea why poeple knock off Dooney and Burke, Abercrombie, Juicy, or any of those brands, but I know there are a ton of fakes out there. When I lived in Greece they were EVERYWHERE.
Good website idea. Good luck!