Repeat this exercise for as many topic buckets as you have. And remember, if you're having trouble coming up with relevant search terms, you can always head on over to your customer-facing colleagues -- those who are in Sales or Service -- and ask them what types of terms their prospects and customers use, or common questions they have. Those are often great starting points for keyword research.
Additionally, there are many situations where PPC (a component of SEM) makes more sense than SEO. For example, if you are first launching a site and you want immediate visibility, it is a good idea to create a PPC campaign because it takes less time than SEO, but it would be unwise to strictly work with PPC and not even touch search engine optimization.