This Mac tip is provided by Mark Greentree and was originally posted on Mark’s blog – Everyday Mac Support. For more of Mark’s tips visit his site, follow him on Twitter, or browse his archive of posts here.
Within iPhoto and Preview, you can select to rotate photographs or documents with the use of two simple keystrokes.
To rotate to the right press Command + R on your keyboard.
To rotate to the left press Command + L on your keyboard.
You can continue to press the keyboard shortcuts to keep turning the item in a full rotation.
Not all applications have this functionality. I did test this feature in Pixelmator, but the commands are assigned to different tasks.