Pixlr is a free and probably the best web based image editor. I will show you how to open and and resize an image, I'm sure you will be impressed how well the web app actually works.
If you use Google services such as Google Reader, Google Drive, YouTube, Contacts, Google+ Circles, Latitude, Picasa Web Albums and a few more, you can download all of your stuff to your computer.
If you are mostly using only one resample image option when resizing images, then you can change the default option to the option you are using the most.