I was planing to make a plugin for JPEG images as well. But until I do, You can work your way out with these plugins...
CW Image Optimizer - http://wordpress.org/plugins/cw-image-optimizer/
EWWW Image Optimizer - http://wordpress.org/plugins/ewww-image-optimizer/
WP Resized Image Quality - http://wordpress.org/plugins/wp-resized-image-quality/
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