Gfycat

Gfycat is gif hosting, with three unique advantages:

Speed - Average is 8 times faster. Unlimited size - No need to use inferior hosts. Have that 25mb gif you want to share? No problem! Nifty features - Play in reverse, slo mo, speed up, or pause and analyze frame by frame.

Gifs are converted in HTML5 Videos, that are 16 times smaller than gif files! And with video, you can also pause, slow it down, speed it up, step frame by frame, or play in reverse.

MORE FEATURES

• Every link includes a gif. Even if delivered by video, the gif is always there. We pick the best format your browser can view, but as a user you can choose to view gif only, or hotlink directly to the gif.
• Global CDN for fast delivery anywhere in the world, backed by Amazon's rock solid CloudFront.
• Not just a simple server: Scalable server system designed to handle content that might go viral. Multiple layers of load balancing and caching with no single point of failure.
• Hotlinking fully approved. Embed your .gif directly anywhere. And even if our servers were all offline, Amazon's Cloudfront would still deliver your file.
• RES integration! If you use Reddit Enhancement Suite, you can play a gfy without even leaving reddit. Just click the Play button by the link (already pushed out to Firefox, Chrome update still pending roll out).

Gfycat was free to use, but there was a subscription service called Gfycat Pro ($3–$4/month), which came with an ad-free experience, and HD GIFs enabled by default.