Compstak has gotten a lot of great press latest, including coverage in Bloomberg, The Wall Street Journal and TechCrunch. From their CrunchBase profile:
CompStak uses a crowd-sourced model to gather real estate information that is hard to come by, difficult to compile, or otherwise unavailable.

CompStak’s wedge into the market is a platform for the exchange of commercial lease comps. Brokers, landlords, appraisers and researchers use their site, and submit comps on completed commercial lease transactions. Users receive points for submitting comps, and may use those points to buy other comps. As a result, CompStak builds a comprehensive database of all of the commercial lease deals completed in a given market, and they sell this data to real estate private equity funds, asset managers, banks, REITs, hedge funds, etc.

TechCrunch loves the idea:

The idea behind CompStak is simple, brilliant, and hugely profitable. Co-founder Michael Mandel was a New York real estate broker when he noticed a disturbing lack of transparency in the pricing of offices and commercial spaces. Some agents and firms had small chunks of data but no one was widely collecting lease “comps” — detailed records of rent prices, square-footage, landlords, tenants, and income that buildings brought in.

Below is a screen shot of results from a Compstak query for comps in the Gramercy-Flatiron submarket.

Right now, their comps are limited to NYC, largely Manhattan. But sources say they've got their eyes set on San Francisco next. Which is probably not a coincidence, as they just landed a $565,000 seed-stage investment led by 500 Startups and are attending its start-up accelerator program in the Bay Area now.