Few days ago I was searching for tool to resize the browser window. It is mandatory that every web developer has one.
The first ten result give the blog of Pete with the solution. Just type that in the browser address bar
and the browser is set to that resolution. Change the numbers of the desired resolution and you are ready to test the new site on different resolution in a quick and easy manner.
Also another solution is to use WebDeveloper plugin for Mozilla if you use that browser. The developer of the plugin is also in the comments in the Pete blog.
Here are some resolution you may try