guideLinr provides rich, Photoshop-like guidelines for any page on the web.
With guideLinr, you can create vertical or horizontal guidelines that will persist by URL. If you visit Google today and add guides, tomorrow they'll be back when you return. Right click on any element to add guides on any edge (top, right, bottom, left, or all).
There are several different color options available, and the color of guides can be changed from the rich context menu available on each guide.
There is an integrated distance measurement tool that shows distance between your guides as you move them. The measurements are now sticky so you can see them wherever you scroll.
guideLinr guides can be dragged with your pointer, or moved with your arrow keys for more precise alignment. Hold Shift while you press arrow keys, and they move faster.
There's an optional "Snap to Element" feature to help align guides to your elements while dragging. There's also a "Snap To Grid" feature that helps create or align guides to a grid of your choosing.
The source for guideLinr is available here: https://bitbucket.org/slobaum/guidelinr/overview