Here's a business idea that I've not seen implemented and which I likely won't have time to attempt:
An app for statistically figuring out which car you should buy.
Like Hot or Not it shows you one car at a time (at random) with a variable (also at random). The variable will be turned into a question. The question will be something like: "What about the price of this?" and it's a picture of a Toyota Prius 2013 with its price. Three buttons to choose: "Too expensive", "About right", "Too cheap".
Next, it's a different car and a different variable. For example, a Volvo XC90 with the question "What about the looks of this?" and, again, three buttons: "Too ugly", "About right", "Too sexy".
On so on... You can keep going, answering more questions, or you can stop and check out your result. Obviously, the more you answer the better the suggestion. You might want to help the user with this so they don't answer too few.
Then when you present the result you can, on that page, show a bunch of affiliate links to various local dealerships where you can buy the ideal car for you. Additionally, if the app becomes successful I'm sure you can easily sell advertisement to car companies who would love to show their ads depending on certain variables. E.g. Honda Fits for those who answer that they want low MPG and small cars.
The algorithm shouldn't be too hard to figure out. I'm sure you can get a lot of mileage just by doing a weighted average on the totals. If you sit down and think about it some more I'm sure you can fit some better established algorithm or something from the neural networks if you lay out your results as a matrix.
That's about it. I don't know where to get the pictures and specs for each car but I'm sure one can scrape from various sites and/or seed some of it manually.
It's the kind of app where you can start small (assuming you have at least 100 cars and 3-6 facts about each car). Also, it doesn't depend on having a bunch of traffic already so you don't need to worry so much about the chicken & egg predicament.
Do you think it could fly?