The popular picture-sharing empire behind I Can Has Cheezburger lets you view, caption and share funny images. You can do this via its sites and, the now, thanks to their API, you can do it via code (technical details at our Cheezburger API profile).
Unfortunately, there appear to be very few developers mashing up LOLs. Who wouldn't want to create something so fun?
The API provides read and write access to the vast database of pictures, both captioned and not. It's not just Cheezburger--the API connects to sister sites, including the popular FailBlog, as well. And you can authenticate users, to include their interactions with the site itself if you want. The API is full-featured, which makes it all the more puzzling that it isn't being used much.
The company ran an idea contest earlier in the year to solicit ways to make its API better. Submissions were private, so it's unclear how many entries they received (though they apparently picked a winner).
One site repurposing Cheezburger content is I Can Has Double Cheezburger, which provides an interface to view many LOLs at once. This is just the tip of what is possible with the API (and this site, which predates the API, may not even be based on it).
An obvious app: search Flickr's API for creative commons photos tagged "cat" or "kitten." Provide an interface to select these photos, caption them with the Cheezburger API and upload for voting. There should be a half dozen sites competing to do this.
Founder Ben Huh has been known to say, with a smile, that "we want you to be happy for 5 minutes every day. That's a pretty low bar." Now perhaps with the Cheezburger API, developers can spread that happiness around (and if you've seen any LOLCats mashups, be sure to let us know in the comments below).