As you know...I mainly just upload YJ photos.
But for the photos that are obviously too huge I use the free Gimp program here:
http://www.gimp.org/
It works well enough for the simple things I use it for.
Cropping Photos:
1. File -> Open
2. Use rectangular tool to outline area to be cropped.
3. Image -> Crop to Selection
Resizing Image:
1. Image -> Scale Image
2. Input sizes needed
3. Hit Scale Button
Sharpen Image:
1. Filters -> Enhance -> Sharpen
(I usually only use 10, but often I don't even use it because it adds artifacts)
Then save the image at 85 to 95 quality (depending on what you need).
That's what I do anyway.