I made up a simple auto image resizing hack.
This code requires ImageMagick installed on your server.
What it does:
If you upload a JPEG image that is greater than 600 pixels wide (or whatever width you choose) this will automatically resize the image. Additionally it will jpeg compress the image (to the jpeg compression setting you choose) and it will add the image width/height into the tag for you.
It makes changes only to the file /wp-admin/b2upload.php
Here's some directions/source:
This code most likely works with PNG and GIF images as well, I just haven't tried it.
Feel free to post feedback, etc.