Rounded edges on photos
For this tutorial, I'll be using this image of Tim Armstrong:
First, open up your image, press Ctrl+J to duplicate the background layer, and delete the background. Now, make a new layer (Ctrl+Shift+N, for you lazies), and drag it UNDER the background copy layer. Next, Select the Rounded Rectangle Tool. Click and drag on how big you want your rectangle to be (NOTE: Make sure that your foreground color is BLACK and your background color is WHITE).
After you've decided on how big you want the rectangle to be, your image should look like this:
Click on your background copy layer and set the layer to LIGHTEN.
Now, go back to your layer with the black rectangle, and select the pen tool. Right-click on your image, and select "Delete Path".
Now, merge your image together.
Now, create another layer (ctrl+shift+N) and drag it underneath your original layer.
Now, select the magic wand tool, and click on the white area of the original layer to select only the white area.
Press delete on your keyboard, and the white should disappear.
And, ta-da! That's it. Its pretty simple. You can do the same concept with the circle tool, instead of the rectangle tool. Let your imagination go wild! :)