When I was interviewing Forrester Research's Claire Powell for our new Case Study (link below), she mentioned they have tested a way of coming up with keywords for Google AdWords:
Instead of just putting ads under obvious terms that describe Forrester's services, Powell's team is trying newsy phrases - such as bits of quotes and headlines that are top of mind for their prospects.
For example, when the Harvard Business Review published a high-profile story entitled "IT Doesn't Matter", Forrester's team tested paid ads using that exact phrase, as well as its opposite, "IT Does Matter".
Claire told me, "For these very specific phrases, the impressions we get are extremely low, but the clickthroughs got up to 10-15%."
Every search expert I know says that often the best keywords are the niche ones. So this is definitely a tip worth testing. Let me know how it goes for you.