I highly recommend subscribing to the "Data is Plural" mailing list. You'll get interesting datasets mailed to you each week! Here's the last one: http://tinyletter.com/data-is-plural/letters/data-is-plural-...

Also checkout "Academic Torrents". Lots of large datasets here, from millions of Tweets, to labeled photos of fish in the wild. http://academictorrents.com/browse.php?c6=1&sort_field=times...