I've got two... I'm not a developer, so if someone decides to make these, send me a free copy!
The first one is simple...
I want to buy an ebook. I log into my kindle app, google play, nook app, and kobo app and look at the price to determine which one to buy from...
Why can't there be an app that compares them all with one search?
The second would probably require hardware, distribution, and a lot of hassle, but could be very lucrative.
So you are in a giant store, like Wal Mart. Where is the ______? You could try to find the one stoned idiot working there... or you could use the in store search app, that guides you straight to the product via some sort of GPS, or more likely, a system wired in the shelves or something.
You could even make it have a function where you have a shopping list, like on Out of Milk, and it finds each item on your list, and creates the most efficient route through the store to collect each item, and then produces a barcode that can be scanned and ring up the entire cartload of crap at once. It would also be easy to tie into a coupon app to do all that in one swipe too. Stores could push people through line faster, meaning lower payroll.
This could revolutionize big box shopping. I'm sure big chains like Home Depot, Wal Mart, etc. would be all over this.