While, searching for psd template to use for my client website design mockup, I found much useful and easy to use plugin for photoshop. GuideGuide is a straight forward addons for creating grids for your website layout. I found it useful because you don't need to recreate or adjust the guides everytime you have a new client which require to have a different layout width than the usual 940px base grid.
How to use?
First, you need to download first the add on and install using adobe manager
Second, Go to the Window > Extensions > GuideGuide and you will find a GG icon on your right side of photoshop.
Lastly, Setup the desire setting i.e Number of Columns , Gutter Size etc.