As you continue to brainstorm phrases some themes should being to emerge. Do you only offer web design or do you also offer web development? Maybe you also offer WordPress development and Drupal development. You might specialize in ecommerce design or small business web design. Perhaps you also offer web hosting. Each of these will likely become a keyword theme around which you�ll build a more detailed list.
Brainstorming will only yield so many words so your next step should be to expand your list through some keyword tools. Here are a few freebies to get you started.