Depends how much money you have to invest into the site, partner development, sales, marketing, etc...
I give away genius ideas every day for free, because I'm poor and don't have money to TM/design them, let alone see a full blown deployment.
Here's a free idea (but company stock is always appreciated)
Turn it into a Nationwide Take-out Food Order Point... How many times are you sitting around the house, you know you want take-out, but you don't know what you did with the menus, or you only have ones for pizza and you want chinese? Most local take-out places don't have websites so you make a site where people can go, enter their street address, see a listing of available take-out joints in their vicinity, click on a specific place to see a complete menu, and then order it directly online.
In theory you could provide an extremely valuable service to customers, take-out joints, and the world in general. Be a hero and a bazillionare at the same time. You charge the customer a fee for using the service, you charge the take-out joint a percentage of the sale, and you charge advertisers to advertise on your site as well as offer preferential listing to take-out joints for a set $ amount or an increased % of total sales.
Of course the hurdles you'd have to overcome would be significant. Developing the site would take a lot of time and effort. Contacting thousands if not millions of take-out joints to get them in the program, figuring out how to get the order details to the take-out joint once the order is placed (since most don't have dedicated internet connections, maybe you just have paid people who do nothing but direct call orders in all day). Then you have to market it to the general public and advertisers...
Business is so damn complicated... I just like coming up with ideas and then selling them to other people to have headaches over...
Btw, if anyone knows of a job opening where I can get paid to just sit around and come up with great ideas, please let me know. Right now I just drive a van around delivering paper. Really looking for a change. haha