Much more than merely resizing, but you can't get much better than the online photoshop express: http://www.photoshop.com/express
http://gui.picresize.com/picresize2/ is the site i use for resizing and i use imageshack for hosting.
For resizing images, use the free image resizer from microsoft power tools. You can resize images in bulk and to whatever size you want. Just select all the images you want to resize, right click, then click resize, and then select the size or set a custom size. You can resize hundreds of images at a time. The program creates a copy of the orginal, so you have both. I have used this tool to resize anywhere from one to hundreds of pictures at a time. I have tried lots of tools, and this is the easiest and fastest one I have ever used. Just click, click, click and your done. Download the tool for free from this link - http://www.microsoft.com/windowsxp/Downloads/powertoys/Xppowertoys.mspx Then I use photobucket to host my images.