If you haven’t installed and tried Irfanview, you are missing out. I work with dozens of graphic file formats on a regular basis, and since I don’t want to open the program that originally created the file to just do a simple view of it (like a Photoshop document, for example), I just use this program. It also has a ton of batch and command line processing features, can open dang near open any format under the sun, and even has a pile of little options and image editing tools and hacks that make life easier. All for free in an 800KB executable (there are about 4 megs worth of plugins that are needed to open some formats, but they don’t slow down the program at all).
Between this and Photoshop, I can open and convert any image I’ve come across, with one exception: really old Corel Draw files. But I’m not losing too much sleep over that.