I've found a website, free, its superb for images. While its mostly for RPG'ers there is lots of things that can be used by budding Vassal modders.
P.S. i'm not affiliated with this site in any way other than finding it absolutely excellent for my own Vassal Modding.

Great sites offering free Images for RPG'ers and Paper Wargamers. Lots of images that are suitable for Vassal Mods.
I urge you to check them out!

http://rpgmapshare.com/
I've found a website, free, its superb for images. While its mostly for RPG'ers there is lots of things that can be used by budding Vassal modders.
http://www.juniorgeneral.org/paper.html
You can find there lots of side view pictures of soldiers, tanks, buildings, etc. There are also some top-down pictures, which might be more interesting for miniature games. Here's an example. http://www.juniorgeneral.org/donated/di ... opdown.png
http://www.dunjinni.com/default.asp