I use Photobucket. It's free and you can organize in different folders or albums and post images on the boards. I actually use this site for sharing other pictures as well. You can set up permissions by folder, too.

http://photobucket.com/

Here is an image that is linked from my Photobucket account:

Other related sites are imageshack (used to use, but didn't like the pop-ups) and flickr.