When using Classic Shell and CSMenu, you can instantly switch back to the default Windows 7 Start menu by clicking the "Start" button while holding down the "Shift" key.

Windows 7 Start Button Changer (W7SBC) is a stand-alone and portable application. Unzip it, run the application, and click on "Select & Change Start Button" to swap your icons.

Windows 7's Start Menu Properties dialog lets you change the function of the power button and prevent recent items from being displayed on the menu. Screenshot by Dennis O'Reilly/CNET ...