Sure we haven't YET found WMDs but there is more compelling evidence that Saddam was getting the pieces in place...here's a quote

Inspectors at the UN's nuclear authority, the International Atomic Energy Agency, have been investigating the worst nuclear smuggling racket ever uncovered, headed by the Pakistani scientist Abdul Qadeer Khan. The operation was discovered two years ago to be selling sensitive nuclear technology to Libya and Iran.

Important straws to grasp:
Dictator with oil money
Has personal vengeance against the US after we defeated him in Kuwait
Violates weapons inspections agreement as part of armistice
Has previously used a WMD (poison gas) against people living in his country

Now and add in the UN's International Atomic Energy Agency knows Saddam has acquired data and equipment that is pretty much not used outside of making bombs.

That's the last straw...

Just cause we ain't found them don't mean they aren't or weren't there. My guess is we'd have better luck finding Saddam's WMDs in Syria.