Long distance investing - Finding the metros to invest

[Matt Cole]

Which strategies, metrics, or websites do you use to select a new city to invest in (rentals)?
Common strategies include assessing the job market (unemployment rate, median income), population (size and growth rate), rents (absolute and % of median income), and housing market (HPI change, housing prices, rent/income ratios, tax environment).

Are there any websites that you have found useful? 
Are there any additional metrics that you've used?