I don't know why Instagram or Twitter haven't done this yet, but I'd love an application that shows me the top 10 newsworthy photos on a world map (Google Maps). So in the US, I might see a few over NYC and LA or maybe another in the Gulf from a recent oil spill. The photos would change based on where I zoom in or out.
The app could look at Instagram's popular page or how many retweets/favorites the photo had on Twitter, etc.
It would be a visual guide to news. Future enhancements would see a scrolling timeline, so you could choose a date and location and see what was going on. And in a few years, the collection of photos would serve as an amazing location-based history of our world.