Animated png or APNG (http://en.wikipedia.org/wiki/APNG). They can be made in GIMP with the APNG Plug-in
But animated Gif’s really are the main one out there – flash kinda took over though, but that isn’t really an image per se.
Also, other alternatives from the same wikipedia page: The MNG file format is a more powerful alternative to APNG, although is a more complex format and has less web browser support.
The GIF file format has better application and browser support than APNG, but it is limited to 256 colors per frame and supports only 1 bit alpha transparency, by mapping one of the palette colors to transparent.
SVG combined with scripting or SMIL can animate vector graphics and can incorporate raster graphics. (See SVG animation.)
Dynamic graphics created with HTML 5 canvas Object can also be animated.
An alternative method for animations in web pages is to use conventional static images and animate them using JavaScript,[22] Adobe Flash, Microsoft Silverlight, Java or other plugin based technologies.