I think a great idea for a website startup would be a grocery shopping organizer. I think stores could pay to have their entire stock uploaded to the site, and then it could also display coupons and sales and whatnot.
The website visitors would be average shoppers. They’d enter everything on their shopping list, and the website would order it according to the store layout, and print out a new list/store map to plan the most efficient shopping route.
People could also categorize items, as buy-every-time essentials, things to look for if they’re in stock, back-up items, special treats, etc. They could save their lists, and maybe even remind themselves to buy things once a month or on some other schedule. Their account would also accept a feed from Twitter, so they could update their lists with things like #shopping buy eggs any time.
I know dot-coms are passe, but this idea seems like it would be solid enough to successfully make money. Stores would benefit by promoting to people who save their lists in their profiles, and by offering coupons and things, and shoppers would benefit by not wasting time.
Of course, everything I know about retail tells me that grocery stores would never go for this, because they want you to wander around and spend as much time in the store as possible, in the hopes that you’ll buy things just because you can’t find the things you actually want. Which, incidentally, is how I got this idea.