There are several tools to resize and edit image files. Here is this cool online tool which reduces the size (not the dimensions) of image file without making any changes to its dimension, resolution, quality etc.

Punypng is an online tool which helps you to reduce the size of an image file up to 35% in some cases.

It supports GIF, JPEG and PNG formats.

I tried reducing the logo generated by default at Twitlogo, and the size was reduced by 7%, for the PNG file, and another JPEG file which was reduced by 20% in size.

Using the tool doesn’t require any account or registration, simply click on upload images button and choose the image you want to optimize, and soon you image will be uploaded and results will appear in front of you telling the percentage by which the image file has been reduced, and you also get a download link for the new file, click on download to get it on your computer.

Give it a try, and have your say in comments, this definitely seems a nice way to optimize the images on your website before uploading time in order to get faster loading.

Try punypng