While creating my first game I came across the need for some sprite sized explosion animations. I tried multiple times to draw them myself, however I just couldn’t get them to look right. So I turned to the web to see if I could find some royalty free explosion animations that I could use in my game. After a little searching I found several suitable sprite sheets like the one below on http://www.positech.co.uk/content/explosion/explosiongenerator.html (The website also features a free explosion generator program to make more).
The animation however was on a sprite sheet that had a solid background and I needed a transparent background. So, I took the time to cut them out using an alpha layer and then saved them to individual files. I have upload the cutout files as I figure it is likely others might find them useful. The below file includes a photoshop file with all the different frames of the explosion on different layers as well as all of the frames of the explosion separated into individual .png files with transparent backgrounds. These images are royalty free so please feel free to use them any way you like.
UPDATE: Couple more free animated explosions can be found here