Well...
There's always bin Laden (or some other spokeman for al Quaeda claiming to be him) enthusiastically allying that organization with Iraq in a news release. But that's kind of an easy one.
There is some evidence that Saddam is financially supporting anti-Kurdish terrorists in northern Iraq. There was an Iraqi training site with a mockup civilian airplane (spotted by satellites) that defectors said was used for training hijackers. Evidence which is circumstantial, and mostly inferential, includes things like terrorists in Iraq having access to weapons and explosives that would probably have to be provided by a state.