What are the key indicators of a good rental market?

[Brandon Turner]

Hey all, I'm doing some research for an upcoming post and I'd love to get some group brainstorming done. My question is: What are the key indicators of a good rental market?  

(For example, schools, crime, jobs, etc.)

Or maybe I can also phrase it this way: What do you look for, in regards to location, when choosing to invest somewhere? 

Thanks all!