The comment was:
"Any suggestions how to effectively argue with Truthers to get through their stubborn skulls?-Steve"
It is rather hard to get things through their stubborn skulls unless you hypnotise them, or wipe their memories somehow or drill a hole in their skulls and connect their brains to some sort of rational thinking machine. But fear not and read on.
From my own experience and also drawing on the experiences of others the simplest answer is that there really isn't anything you can say that can change their minds.
The current opinion of the JREF Forum (where I go to talk about things like this) seems to be that the "Truth" movement is dying. Recent things that were touted as life-changing or something like that, like the release of Loose Change: Final Cut were complete flops and NIST's WTC 7 report will be a complete failure to them when it is released, currently they are saying it will be the key, they will probably claim government tampering or something when it doesn't support their ideas. The next section will be much better, I promise (the most important thing is in the bold print).
There would still be people floating around that you can convince, and there would still be plenty of fence sitters who have just managed to catch on. These are people that can be convinced but it may take some time.
For many debunkers it is the fence sitter, not the CT, that engages them into these debates, but you can convince a CT at times.
Information will be the key to convincing someone, and a lot of patience and tolerance (I have snapped before but that was more because the CT had turned to lacing responses with ad hominems). If you go here, you can find pretty much all the information you need on their points.
One of the strange things about the 9/11 CT is that it is something of a hybrid. It's what you get if you have someone who is paranoid about the government, crossed with pseudoscientist, crossed with creationist.
I have come across some good sites reading in my free time about various things that have helped.
Phil Plait's On Debating Pseudoscientists is invaluable. Especially this line:
"What I have found is that there is usually a core set of claims, the "big ones" upon which the rest of the other thousands of claims rest."
You will find that with these CTs as well. For example Chris Brown of "C-4 coated rebar" fame basically rests on two main premises. The first is that there was a concrete core, and the second is that C-4 will last for 30 years in a high alkaline environment. If you can disprove either point you can convince anybody. Anybody that is except Chris Brown. These claims will exist in all the theories and aren't hard to work out. These claims are protected by the simplest of logic.
If you have had any experience with creationists then you already know some of the techniques being used. If not this article will be very useful (when you get to "The scientist / informed lay person debates within constraints that Creationists do not bother themselves with, i.e. sticking to the facts." just replace on the list "Creationist" with "Truther" the rest is an interesting read, but not as relevant unless you happen to be arguing in real life), as is anything from talkorigins.
Finally, and I probably should have put this first, is Debating with a Conspiracy Theorist
I found this in my earlier days of arguing. It contains pretty much everything that you need to watch out for.
To summarise, arguing with a "Truther" is basically arguing with a fundamentalist Christian you will most likely never convince them, but it is possible.