I resize my images around the 800 x 600 mark (portrait or landscape orientation)...give or take a few pixels either way.  I use the SAVE for WEB option in Photoshop CS3...and try to keep the file size under 250kb.  You can experiment with different JPG compression settings in realtime and see the results.  Note this option strips out the Exif data  too. (camera settings and whatnot) 

Here's a couple tutorials for reference.

www.elated.com/articles/the-save-for-web-feature/

www.impulseadventure.com/photo/save-as-save-for-web.html

Hope this helps a bit.

J:woot:e