Price: Free !
This is a simple but very useful extension developed by the User Interface Designer and Front-End Developer Gaston Figueroa.
It does exactly what you see in the image.
Layer Guides places guides around a layer (top, right, bottom, and left sides) and also on its vertical or horizontal center.
However, the best part is that it detects when you apply styles that fall outside the boundaries of your layers. For example, if you apply a shadow or an outside glow to a layer, you might want the guide to be where the effect ends. Layer Guides allows you to do that. And it is completely free.
To download and get more information please go to:Layer Guides