GuideGuide for Photoshop
Whether you need to create responsive grids, measure columns with margins, or just find the middle of things, GuideGuide has tools that will make your life easier.
Every feature works with your document, artboards, layers, and even your selection, so that you can add, remove, and duplicate exactly the guides you want.
You can also take advantage of it's handy abilities to add guides at the top, left, bottom, right, and midpoints of your document, artboards, or selected layers. You can even duplicate guides between artboards and documents.
GuideGuide has been around since 2010, has created millions of guides, and is Photoshop's most installed third-party extension.
Follow GuideGuide on Twitter for occasional announcements about new releases: https://twitter.com/guideguide