Need Some New Keywords? Do Thorough Site Review
Your FAQ pages can offer insight into long-tail keywords that customers may be navigating to, and provide a good source for PPC ad copy. News update and press pages can also offer new keywords, since if your company is appearing at an upcoming conference, you can snag searchers with "PPC summit [company name]" queries, and so on.
And take another look at your product/service pages, this time with an eye for the kinds of problems they offer a solution to. For example, people in need of landscaping may not enter "lawn care" or even "landscaping" during a query--they may be in search of a solution for their "overgrown hedges," "lawn rehabilitation" or even" dead grass removal."