Photo is not the most sophisticated image viewer out there, but it offers a perfect blend of simplicity and flexibility that makes it a handy utility, indeed.
The best piece of software for simple cropping of images seems (to me) to be Shotwell Photo Viewer, especially as I find GIMP's cropping methods (AutoCropping & Zealous Cropping) incomprehensible. I can start Shotwell Photo Viewer by right clicking the image file (in Nautilus).
I'm looking for a way I can view .CR2 raw photos without opening GIMP. It seams overkill to open a full-featured editing program just to view a photo. I'm looking for a program that will allow me to quickly view the photo and maybe cycle through them using the directional keys...