There are a lot of approaches for resizing images (ImageCache, Image, iMCE, and many others). However when building a site for a simple user (no previous web experience), I found that all of these approaches required too much effort on the part of the end user. Why can't a user just resize an image in their WYSIWYG, and not worry about the size of the image at all? That's the goal accomplished by the Image Resize Filter. Despite its extremely techie-sounding name, it's ridiculously easy to use. It provides inline resizing of images to match any <img> tag in any HTML inserted in any Drupal textarea that supports filtering.
Image Resize Filter Project Page: http://drupal.org/project/image_resize_filter