Some weeks ago I wrote that Google had rolled out a new design for their search page. Later it turned out to be just a test run. The real changes went live yesterday. Anyway, if the sidebar is annoying you and you wish to go back to the old design, this is what you need to do.
If you use Firefox you have another way of achieving the result – through the Stylish addon. Install this addon and then add the following script to it. Save it and you are done.