RightGIF - Less noise, better GIFs. A better /giphy for Slack.
Slack Meme Bot - Spice up your team conversations with memes
VixT on Slack - The best video mashup app now on Slack.
SnipandShare for Slack - Quickest way to share bugs, ideas, links or gifs to Slack
Yarn for Slack - Drop TV and movie clips into your Slack chats
GoGifApp - Free Slack GIFs App, multiple images to pick from at once