Related: How to Create GIF Cinemagraphs
To create an animated GIF online, all you need is a set of images (in any format like jpg, png, etc) and Glickr.com, a free site that will convert them into an animated GIF movie of predefined sizes that you can use as profile avatars or post them on blogs.
Individual images can be as large as 1 MB and you may directly grab your Flickr pictures inside Glickr.com. You may also change the speed of your animations [like how frequently the image transitions happen]
Some people find animated images as annoying as blinking webpages but they are a good medium for sharing photo slideshows in situations where Flash is not an option.