Just off the top of my head I can think of a half dozen really easy ways to weaponise dangerous chemicals.
The end results tend to be nowhere near as effective as simple explosives.
As an example, the latest chlorine bomb attacks in Iraq. 3 vehicle mounted bombs, 8 dead. Given that a single car or truck bomb in Iraq often kills upwards of 50 people, the chlorine attacks were not a success, although no doubt the fear they cause is of some benefit to the terrorists.
Another example is the Tokyo sarin attack. 10 bombers, 11 kg of sarin, 12 dead at the height of rush hour on the Tokyo underground.