Here's really slick video of some graffiti bombing with P.Do, Eager, and Tase. It's a really cool video of some skilled artist doing their thing.
Here are some graffiti resources for learning that you can use today.
Learn Graffiti Guide - A guide to learn graffiti in PDF form.
Spray Paint Art - Make money learning how to do serious spray paint art, beyond graffiti.
Amazon's Listing of Books - Amazon has a ton of books on graffiti, click here to find them as low as a penny each.