The Dec CPI came out today: down .7 percent (at monthly rates) from Nov. The Dec 2008 CPI is a bit lower than the Dec 2007 CPI: 2008 was a year of (a bit of) deflation.
This gives me enough data to make a confident forecast for the 2008 Q4 GDP deflators that will be released by BEA this month. The forecasts are Q3-Q4 percentage changes at annual rates.
GDP deflator: -3.3 percent
PCE deflator: -4.6 percent
GPDI deflator: -0.8 percent