i've used ImageMagick and have been very happy with it. It comes with FC3, although i don't know what other distros it comes with. If your distro doesn't have it then you can download it
here. You can animate PNG files with it and GIF. PNG is not accepted by all browsers though, at least not the animations i don't think. i am not sure all of the file types that support animation but you can try any file type with this program, it's a question of whether or not that file type supports it though. The program will bind the files either way.
If i remember right, they've also got tutorials that you can use on their site and descriptions of what each command can do, it's also in the man file though (this is a command line program). You can do so much with this program, things i didn't know you could do until i started using this.
Good luck and have fun.