Sources for data mining rents by zip code

[Christopher Canning]

I'm looking to bounce SFH sale prices against rents. I've found plenty of sources for home sale prices that I can easily get in a downloadable format (csv) but I can't seem to find a downloadable database of rents vs zip code/neighborhood. I see that city-data as well as truila have heat maps, but I can't find a way to download the information and I'm not sure what database they are using to generate the maps. Any help would be appreciated.

Thanks,

Chris