Faststone Photo Resizer is free, has lots of options and does a great job of resizing images, whether it's just one image or whether you want to batch resize a large number of images at once. Although I have Photoshop, I frequently use Faststone Photo Resizer for resizing tasks. Incidentally, the folks at Faststone also have an excellent image viewer, which is unrivalled in my opinion - Faststone Image Viewer
I regularly use this to browse and search my raw image files (and other image format files too) as it's faster than Adobe Bridge on my machine.