I thought this page could be useful as a guideline for how discourse is carried out in this forum. It identifies a number of logical fallacies that are frequently used in discussion where peoples opinion differ.

http://www.intrepidsoftware.com/fallacy/toc.htm

As a short list.

Attacking the Person
(argumentum ad hominem)

Definition:
The person presenting an argument is attacked instead of the argument itself. This takes many forms. For example, the person's character, nationality or religion may be attacked. Alternatively, it may be pointed out that a person stands to gain from a favourable outcome. Or, finally, a person may be attacked by association, or by the company he keeps.

This is one, that as a moderator I will simply not allow as it clearly violates the AUP. If you disagree with someone, feel free to attack their arguments as vigorously as you want. You should never attack the person themselves under any circumstance.

By the same token, if someone is confining themselves to attacking your argument, try to have a thick skin and not take it personally. It isn't wrong for people to disagree on something, as long as that disagreement is handled properly. (If they are singling you out and try to shoot down any and everything you say, that may qualify as harassment under the AUP and will be dealt with if it occurs.)




This one is surprisingly common.


Straw Man

Definition:
The author attacks an argument which is different from, and usually weaker than, the opposition's best argument.


This basically amounts to attacking a week version of someone's argument and claiming victory over the whole argument.



Another one that is quite common.


Begging the Question
(petitio principii)

Definition:
The truth of the conclusion is assumed by the premises. Often, the conclusion is simply restated in the premises in a slightly different form. In more difficult cases, the premise is a consequence of the conclusion.


Another common one in discussions about micro-processors

Composition

Definition
Because the parts of a whole have a certain property, it is argued that the whole has that property. That whole may be either an object composed of different parts, or it may be a collection or set of individual members.


A few more:


Coincidental Correlation
(post hoc ergo propter hoc)

Definition:
The name in Latin means "after this therefore because of this". This describes the fallacy. An author commits the fallacy when it is assumed that because one thing follows another that the one thing was caused by the other.


False Analogy

Definition:
In an analogy, two objects (or events), A and B are shown to be similar. Then it is argued that since A has property P, so also B must have property P. An analogy fails when the two objects, A and B, are different in a way which affects whether they both have property P


There are many more examples as well. The page also has examples of each to help you recognize them when they occur, and even has pointers about what to do when you see them.