This was a good site I used the other day as I needed to shrink a picture to include into a Textexpander snippet. I just simply uploaded the picture to http://www.picresize.com. Chose the option from the list it presented to you and then downloaded the new shrunken image.
The site is quite noisy with all the adverts all over the site, but as a free utility it is a good site to have to hand.
I am always interested in feedback so please feel free to add any comments, or you can mail me here. If you would like to submit a quick tip with full credit and links back to your site then also feel free to contact me.