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 employees on the front lines -- like Sales or Services -- 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.
Earlier, I wrote a post about the use of long tail keywords. Focusing on long tail keywords could be a good strategy, especially when trying to rank in a highly competitive market. But how do you decide on which (long tail) keywords you want to rank? This post will give you some handy tips and keyword research tools to make your keyword research a bit easier.
Long Tail Pro is a keyword research tool that helps you quickly find low competition keywords for your website.  In particular, the tool is built for people doing SEO (search engine optimization) as opposed to people doing paid ads (Google Adwords PPC).  I'm sure there are some advertisers that use the tool for paid ad keyword research, but the tool was built for SEO keyword research.