Mac: We've talked about a variety of ways to make your own animated GIFs, but if you're looking for an incredibly easy way, PicGIF does the job.
GIFs can be a little complicated to make, but PicGIF makes it easy enough that anyone can do it in a matter of seconds. You can edit existing GIFs, turn videos into GIFs, or turn photos into GIFs. You can also easily add text, trim the length and more. If you prefer, check out a demo on their site if you're interested and don't want to shell out the $6.49 (which is actually a sale, it's usually over $20).
PicGIF ($6.49 -- on sale) [Mac App Store]