How to deal with faith
"Maybe I don't have any arguments, but I have faith, and you can't take that away !"
From an evangelical perspective, you're still at the beginning there. Of course the Christian has faith, that's assumed as a matter of course. The question is, why ?
From a debate/discussion perspective, many people think this is the end and that there is nothing left to say, but it really isn't and there is still plenty to say. As I've discussed recently in the classification of the positions, belief is not an ontological position. The idea that one has faith is not an ontological statement, but a personal appeal. There are believers of every religion because one's religion is determined by parental indoctrination, not by the evidence.
So the first answer one should give to such a statement is "why are you bringing your personal appeal in a discussion about facts ? We don't care whether you have faith or not". To invoke a personal appeal against arguments of fact is a cop-out.
Of course, the emotional weight of the belief is such that this is unlikely to to convince anyone. And if you are trying to convert someone, it's the wrong thing to say. But it's a perfectly natural reply in a philosophical discussion. Why should we care about someone's faith ? We should care no more than we would about someone's scientific position. Truth is not a vote.
There are many places we can go from here :
* You can use the subjectivity of belief-forming experiences to show how fragile the concept of faith is. "Religious experiences" are only assumed to be of God, or even "religious", because of the believer's presuppositions, and so on and so forth.
* You can also use the dice analogy - you roll a die, and either assume what the number will be based on your favourite numerological belief (faith), or use your senses to look at the die and see what number it is (reason) - to prove that the Christian does not take faith seriously. Parallel to that, you can ask them in general how many things they have faith about, or why they don't have faith in the Spaghetti Monster or other gods.
* You can point out that Biblical characters did NOT need faith, as they had material evidence of the existence of God. Why aren't we all given what Abraham or Paul had ?
* You can take the argument tack and interpret faith as a variant of the arguments from belief, and argue that materialism can give an account of the person's faith, disproving the connection between the personal appeal and the ontology.
* You can attack it outright with materialist apologetics and show that the Christian could not have such a faith without concepts (such as the idea of what "God" or "Christianity" is) and without the nature of whatever it is they use as support.
But never let the Christians off with the excuse of faith. It is really no different from any other personal appeal, just more generalized. If you have any other ways to deal with faith in a discussion/debate perspective, post them on the comments and I'll add them.