If you are extract brewing, there is a limit on how light your beer will actually get. The process of making malt extract naturally darkens the malt a bit, making it hard to get a really light color in the finished product. In addition, the process of boiling will make the beer darker as well (for you chefs out there, it's the Malliard reaction). You can resort to using some adjuncts like rice syrup solids, but they will affect the final flavor of your beer. Your best bet is to use the extra-light DME and don't use any dark specialty grains. Nothing darker than Crystal 10, and keep a light hand on that. Stick with a 60 minuted boil to minimize darkening due to boiling. You may find that adding stuff and altering your processes trying to make the beer a lighter color causes you to sacrifice some flavor. Not a good trade. Unfortunately, the best way to make a light colored beer is to go all grain.