Weekend Widget: Irfanview
Irfanview allows you to view most every bitmap format ever invented. Together with the plug-ins that can also be downloaded for free, I don't think I've found a format it couldn't open. I use Irfanview often to quickly flip through a folder full of images. I'll admit that I probably don't even use 10% of the features.
It can be used to convert images and I've used this occasionally when I need to convert a file for later editing with Corel PHOTO-PAINT. Other features like optimizing, slideshows and batch processing have also gone unused on my system. When I look at the feature list and see all of the things I don't use, I realize just how much power this little program packs. Download a copy for yourself and let me know what you like most about it.