You can also use the Keychain application to give you a menu option to sleep the display.
Also note that the hot corners feature is more useful than it might appear. When you're setting them up, you can hold a modifier like control, shift, option or command. If you do that, the corner will only trigger when you hold that key and mouse the mouse to the hot corner. Personally I have the screen saver set to control and lower right, so I don't enable it by mistake.