Old joke: How do you know Bush is lying?
The Center for Public Integrity and the Fund for Independence in Journalism have released a report finding that the administration issued at least 935 false statements in the two years leading up to the invasion of Iraq as "part of an orchestrated campaign that effectively galvanized public opinion and, in the process, led the nation to war under decidedly false pretenses." Administration officials stated unequivocally on at least 532 occasions that Iraq had WMDs or was trying to produce or obtain them or had links to al-Qaida or both. Neither of those claims have turned out to be true. Specifically named in the report are Bush, Cheney, Rice, Rumsfeld, Powell, Wolfowitz, and the White House press secretaries Fleischer and McClellan.
[The report website is taking a bit of a beating at the moment, so you might have to be patient if you want to read it]