I like the heavy-handed artistic style that seems to be common in a lot of them: simple color schemes paired with dire imagery. Its very utilitarian and inspirational at the same time, and I find them beautiful in a way thats hard to put a finger on.

Any way, if you too wish to browse some propaganda posters, you can find a couple of nice repositories on Flickr:

War Posters WWII posters

And I've included my favorite with this post.