Here's a good one too:

Microsoft Power Toys

If you click that link, it takes you to the microsoft power toys web page. On the right side of the screen, there is a list of downloads.

About halfway down is the "image resizer". It's a quick little download but it's very pimp. Without even opening a picture you can right click its thumbnail and resize it. It gives you four standard sizes you can resize to, or you can click "custom" and size it to whatever you want. Best of all, it creates a NEW picture that's the new size. The original is untouched.