Jing
Jing simplifies creating screen captures and allows you to crop and annotate your screen images. I find myself using it a lot to save photos of bottles that are protected (where you cannot right click and use the SAVE AS command). The basic edition is free; a premium product is available for short money but I never find that I need the advanced features. And, best of all, it is really easy to use. Download from http://techsmith.com
Picasa image editor
Now available free thanks to Google. Visit the Picasa site.
Irfanview
Another amazing full-featured image viewer & editor – free!
FastStone
A fast, user-friendly image browser, converter and editor which has an impressive array of features that include image viewing, management, comparison, red-eye removal, emailing, resizing, cropping and color adjustments. Free. Visit their website.