Announced on the website of the Department of Provincial Administration (DOPA) is the official population number of Thailand as of December 31 2008.
According to this announcement, which is based on the registration data, the kingdom had 63,389,730 citizen, 31,255,869 (or 49.3%) male and 32,133,861 (50.7) female - Kathoey are apparently not counted separately. However, DOPA has not yet updated the full statistics of population per province, district and subdistrict, the latest it has there are the data as of December 2007 (exact day not specified). Last year this was put online beginning of February, so it should be available soon.
Comparing the population numbers of 2007 and 2008, one sees an increase of 35,1483 or 0.56%, which is about the same growth rate it had for the last years. When plotting the data from 1993, the first year it has these full statistics at the DOPA website, one sees a steady increase. The decrease by 1 million in 2004 was probably a statistical artifact, and not a real population decrease.