Historical and expected returns

 provides historical market data as well as estimates of future market returns.

Burton Malkiel
Burton Malkiel, author of A Random Walk Down Wall Street provides historic asset class returns.

Robert Shiller
Robert Shiller is a Professor of Economics at Yale University. He maintains multiple historical market data spreadsheets, including the following:
 * U.S. Stock Markets 1871-Present and CAPE Ratio

Aswath Damodaran
Aswath Damodaran is a Professor of Finance at New York University. He maintains various corporate finance and valuation spreadsheets, including the following:
 * Annual Returns on Stock, T.Bonds and T.Bills: 1928 - Current

John Bogle
John Bogle with reasonable expectations for stocks and bonds over the next ten years, using his own "Occam's razor" model. Note: Bonds expected return assumes accepting moderate additional credit risk and significant interest rate risk vs. the U.S. Treasury 10-year note.

William Bernstein
William Bernstein with a summary of reasonable expected returns over the next ten years, derived from the dividend discount model, published in 2014.

Bernstein's estimates in 2002 are below:

Rick Ferri
Rick Ferri, author of All About Asset Allocation.

The table below is an expected return for all major equity and fixed income asset classes over the next thirty-years. It could be used as guide when constructing a long-term diversified portfolio.