Kiplinger's Personal Finance pointed me to the two great resources of the overall P/E ratio of the market:
Dow Jones Industrial Averages
S&P 500 (Excel file)
The first report reads that DJIA is sitting on 20.6 times trailing earnings and 17.6 times forecast earnings. (Furthermore, DJIA components collectively has a price/book value of 4.02 and dividend yield of 2.01%.)
The second report shows that by the September quarter (the last quarter the actual data is available), S&P 500 was at 25.8 times "as-reported" earnings. By the end of 2004, S&P 500 shall be at 24.3 times earnings with the current forecast.
By all means, the current overall valuation of the market is not cheap. As shown in a historical S&P 500 P/E calculation, S&P 500 P/E ratio was 23.5 on average between 1989 and the first quarter of 2003, and was only 15.5 since 1935.