Use Preferences / Guides, Grid & Slices to control the Style, Color, and Grid line spacing and subdivisions. Yes, this means that guides can be a soothing neutral gray, not Cyan or Magenta!
To quickly display rulers at the top and left of an image, click the View Extras icon in the new Application Bar in Photoshop CS4 and select Show Rulers from the drop down menu, or use the keyboard shortcut, Command (Mac) / Control (Win) + R to toggle the rulers visibility. Command (Mac) / Control (Win) + “;” toggles the visibility of guides and Command (Mac) / Control (Win) + ‘ toggles visibility of grids.