EPS-HDT

That's a really unfortunate name for something that is actually quite useful: EPS-HDT by Headwater Economics aggregates tons and tons of socio-economic data into MS Excel workbooks. It currently runs as a MS Excel Add-In, but a web-based version should be available soon. Another option is Social Explorer, especially if you have access to the professional edition.

http://headwaterseconomics.org/tools/eps-hdt