The IsometriX engine has a demo of a walking figure. You might be able to use its sprites for your test.
http://www.mygale.org/hatti/MrY/isoxeng.html

Does anyone know a site with some pictures of sprites that I could use just to test my engine? What I'd need is a character which has a walking animation in at least the eight directions of up, down, left and right and the combinations. A few additional actions such as walking with a secondary animation, such as a weapon in hand, and swinging the weapon wouldn't hurt.

The ideal case of course would be a collection of different kinds of creatures, buildings and terrain features, but even a single character would suffice