CoolMiniOrNot now supports pictures of unlimited width, and file size has been increased to 1024kb.
The way this works is images are still restricted to 650 pixels wide on the page, but will be stored at whatever width you uploaded them at. While browsing, if you see a icon, it means that clicking the image will automatically bring up the full sized image for your viewing and voting pleasure.
Do note, the 1meg file size limit is still a hard limit, so do try to keep image compression reasonable if you are uploading pictures. Remember, pictures that are too large may actually hurt your score! :D
I would suggest that you keep the max width of your pictures to under 1200 pixels so that viewers will not need to scroll horizontally to view your miniatures in all their glory.
Try this url to get an idea of how it looks: