So an MIT student is doing a research project to see whether GIFs are a language. You can vote and contribute here: [url=http://gifgif.media.mit.edu/]

The really fun part are the results. He's cataloging which GIFs have been best voted to reflect a particular expression. Which makes them a perfect place to find reaction GIFs. 

[url=http://gifgif.media.mit.edu/results]

Enjoy, friends.