Andrew Ingram's GridMaker is a brilliant script for Photoshop that can be used to automatically generate guides in your PSD.

The script allows you to enter the series of columns that should be laid out both horizontally and vertically. Then you set the maximum dimensions for the canvas. To generate a Blueprint grid, for instance, you'd enter "30,10" to create a PSD with a series of repeating columns of alternating 30 pixel units and 10 pixel gutters. You can set any number of columns in the series.

The script is saved into your Photoshop "Preset / Scripts" directory and is summoned by selecting "File $gt; Scripts."