TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
Compressnow - Compressnow is a web service used for compressing the image to be used for different purposes in the websites or promoting the products as this is a problem for both web developers and end-users.
ImageOptim - Faster web pages and apps.
ImageRecycle - Image/PDF online compression service.
TinyJPG - Compress JPEG images with perfect quality and file size
ImageResizer - Free online app to crop and resize images