I stumbled across this site yesterday when I needed to resize an image for a blog post. This site is great for people like me who can't figure out how to resize photos with complex applications, and are too cheap to buy Photoshop.
There are 3 basic steps:
1. Upload your image
2. Use the buttons to set the image size and/or crop
3. Click the resize button and download your new image
It is simple and worked out well for me. Check it out at http://www.resizeyourimage.com