I noticed no links under the image viewers and would like to make a suggestion for a link to a free image viewer application that is already portable. You should drop those guys a line and see if they mind you linking to their page.
The application is very well written and can do limited image manipulation. Far better than Irfanview in my opinion. (No, I don't work for xnview, just glad to see such a beautiful peice of work made available to all).