Animated GIFs kind of come and go in popularity, but seem to be having a bit of a resurgence lately. GifMill is a free app for your iPhone or iPod touch that lets you take photos and create animated GIF images you can share with friends via Tumblr, Twitter, email or text message.
You can also use photos from your camera roll or even use short videos. Up to 100 stills can be used to create the GIF. Once the frames are selected you can control the frame rate and quality, and rearrange or delete frames from your sequence.
I tried the app with pictures of my parrot, and got a nice result without any trouble. The app offers an in-app purchase of US$0.99 to add text, but I didn't bite. When you email an animated GIF it plays right in the message, even on an iOS device.