ImageViewerCMPlugIn

It's a contextual menu item that'll make it a snap to view all images in a folder, as a slide show, without the help of any other program. JPEG, GIF, TIFF, BMP, PNG, PSD, AI and EPS are supported, and you even get access to handy controls such as zoom, rotate, and view image info. It is a shareware (as in "cheap"). The unregistred version is not crippled in any way.