GuideGuide: useful guide placement tool for Photoshop

I'm posting this as much for my own future reference as anything, but GuideGuide by Cameron McEfee is a really useful guide generator plugin for Photoshop.

It does stuff like applying guides to mark the centre of the document as well as guides for a whole grid layout, complete with rows, columns and gutters.

If you design with grids, this should save you a good amount of time when first creating your design files in Photoshop.