Frank mentioned this NYP article about how some companies are buying sites outright rather than increasing their AdWords bid prices. I expect this to be a large and growing trend for at least a couple years. As Google gets more efficient at pricing the ads they increase the value of the top ranked sites that sit alongside those ads. Internet Search Metrics, quoted in the NYP article as Internet Search Management, is providing audits on the competitive landscape of search

ISM's audits track the top 4.5 million search phrases on Google and Yahoo!, a total of 7.3 billion searches a month, to determine which companies across 50 business sectors pop up most frequently in the top three or four positions in natural search. ...

The ISM audits, to be released in London, break down which of 50 business sectors are locked up - that is, have large chunks of natural search dominated by a handful of companies - and which are wide open.

I have not yet seen any of the reports, but the network is still young. If you love marketing, are in tune with web trends, and are well funded I am guessing that many of the markets that appear locked up are still wide open.