returns over the truly long run in the American stock markets have been 10% nominal with inflation of about 3%, for a real return of about 7%.  This is from data I saw in the 90"s.

Returns from the last 20 years have been far higher, as Jeremy Siegel"s recent WSJ article showed:

Since 1980, the return on Dow industrials has averaged 13.89% per year, significantly above the 13.06% recorded for the S&P 500, a benchmark that many active money managers find difficult to beat.

The S&P 500 would be the better judge of the market as a whole (though historically small cap stocks have outperformed).  But inflation has likely been less than 3% since 1980, so the return over this time frame is abnormally high in real returns,,,,about 10%.