The MIT Center for Real Estate along with Real Capital Analytics has developed a commercial real estate index designed "with the objective of supporting the trading of commercial property price derivatives."
The index includes the four major property types and is computed on a monthly basis, starting with July 2001. Each property type, including retail has a separate index computed on a quarterly basis. Data can also be viewed on a regional basis.
It's a fascinating idea and will be interesting to see if it catches on. Last year, Standard & Poor's and Robert Shiller, of Irrational Exuberance fame, launched an index for based on single-family housing for a similar purpose.