Sizer is a freeware utility that allows you to resize any window to an exact, predefined size. This is extremely useful when designing web pages, as it allows you to see how the page will look when viewed at a smaller size. The utility is also handy when compiling screen-shots for documentation, using Sizer allows you to easily maintain the same window size across screen grabs.
Rocky Oliver mentioned it a while ago, and I’m using this great tool for a couple of years. It is my #1 freeware tool. You can download Sizer from here