Here's a tactic that Matt and I have been using for a while, and think it would probably be useful for the kind of online, anonymous arguments that inevitably crop up on websites like the Huffington Post, but others as well.
The most common argument that any Palestinian supporter or Israel hater will use is to simply start talking, ranting or copying and pasting a large block of text about the poor, suffering Palestinians. It can be about any topic, any subject, from any point in time, and all of their fellow travelers will praise them. But the trouble is that this is a two-sided conflict. So how should you respond?
Respond by saying: "Wow. It sounds like the lives of the Palestinians are really difficult. Maybe they should consider making peace?"
Although this may come off as callous, it's also the truth: if the settlements are stealing Palestinian land, why don't the Palestinians make peace and stop the settlements? If the Palestinians don't like people dying at the hand of IDF soldiers, why not make peace so that they won't be fighting each other any more?
There are two ways that anti-Zionists usually respond to this argument. Either "We can't make peace because of ________," or "how are we supposed to make peace when Israel is doing ________." That blank is most often filled by settlements and pizza analogies, but it can also be blockades and "occupation." When they say this, what they are really saying is that settlements, for example, is more important to the Palestinians than peace. If you had any other group of people saying that land is more important to them than the lives and welfare of their people....well, that's also pretty callous.
This would seem like a good tactic because they are deflecting back to Israel, but now the conversation has stopped been them screaming lies about Israel and you pointing out they are wrong. Now they are explaining why the Palestinians are justified in refusing to make peace and you telling them how ridiculous that is. The focus of the conversation has shifted to Palestinian intransigence, which is how it should be. Palestinian intransigence is the root cause of the conflict and in turn their own suffering, and that is what we should be talking about.
Let's not forget either that other people have made peace and stopped fighting after being treated waaaay worse than the Palestinians. Japan had not one but two cities almost completely wiped out by atomic bombs and they were still able to move on and secure a better future for their country. The Palestinians seem to enjoy finding excuses why they have to keep fighting (for "justice" or whatever) and there's no reason why they shouldn't be called on it.