Better Grids 2

Better Grids 2 provides three panels that assist you in creating pixel perfect layout and grids with guidelines in Photoshop. The Grid Builder panel lets you define columns and rows, gaps between them as well as the margin to the edge. It's also possible to control cell weights or set specific aspect ratios. Once you're done, you can render the grid as frames for easy drag and drop placement of your designs.

If the layout you're looking for is a bit more complex than a typical grid, try out the Layout Builder: Specify exactly where each guide should go and save your own presets.