Salary.com - basic salary information for free
SalaryExpert - free salary and cost of living reports
Climbtheladder Salary Guides - Salary Insights for things like experience and location.
Sperling's Best Places - cost of living and salary compensation. Offers good tool to compare economy, housing, health, crime, education, climate, and transportation in two cities.
U.S. Bureau of Labor Statistics - employment and unemployment statistics; information on salaries