I find myself in Photoshop pretty much every day in the office. As our web team moves increasingly to a responsive, grid based framework, design work has to match grid structures perfectly, hence the importance of grid guides or layers to keep things on track.
But Photoshop doesn’t make quick guide generation easy out of the box. Enter GuideGuide, a free tool by designer Cameron McEfee. Install it as a Photoshop extension, and with just a few clicks you’ve got simple horizontal or vertical grid guides based on percentages or pixels.