Top 3 keyword categories with the highest search volume and CPC, via WordStream:
Insurance (example keywords in this category include “buy car insurance online” and “auto insurance price quotes”)
Loans (example keywords include “consolidate graduate student loans” and “cheapest homeowner loans”)
Mortgage (example keywords include “refinanced second mortgages” and “remortgage with bad credit”)
97% of Google's revenue comes from advertising on Google sites. In the last four quarters alone (Q3 2010-Q2 2011), Google brought in $32.2 billion in total advertising revenue.