Online Resources with Rental Information

[Andrew Jervis]

Does anyone have any suggestions for websites or other online resources that are good in determining rent estimates in different areas? 

I want to develop my own analysis of expected rent as opposed to what MLS listings have. I use craigslist and city data as a baseline but want to make sure i'm not missing out any great resources.

Also, any other can't miss general REI online resources I should be taking advantage of?