This is an AWESOME little tool. I spend quite a bit of time adjusting window sizes for screenshots at work - and this is going to be a BIG time saver.
I work with proprietary software that doesn’t resize using external apps. This tool, however, gives you dimensions as you resize - so you can just drag the corner to the right size! So simple, but SO useful.
http://www.brianapps.net/sizer.html