1) Quote mining: People who quote something, out of context from a secondary source are usually doing something fishy. Consider a review on a book on evolution; a typical tactic is to find a random review and then quote something from the reivew about the book and hold it as fact as the books 'opinion'. This tactic works on two levels, the first is it confuses the original citation making it much harder to tell if the individual is lying if they haven't actually read the book or not. Many people are not willing to bother looking up the entire book, so the quoting from a secondary source just makes it even less likely for someone to go to the work of verifying the claim. The second part is that if the book is rare or hard to get it makes it impossible to refute the point.
This is usually done by people who are merely parroting the opinion of someone else, usually from said reviewer particularly if the reviewer had a bias against the original book. The other form of quote mining is even more insidious. This time the citation from the original book is given, but a quote is cherry picked completely out of context and the indivdual knowingly misrepresents the opinion of the original author. Typically this is done as part of the logical fallacy of an 'appeal to false authority' to try and buy false credibility, or just to try and degrade the credibility of actual authority (such as an actual biologist working in that field of research).
2) Appeals to false authority: Now I've mentioned it, this is one that makes itself blindingly obvious extremely quickly. Typically, you end up with people citing their PhD they got from a diploma mill as is the case with Kent "Dr. Dino" Hovind. You can easily spot these by simply noting people quoting a chemist on a biology topic, an historian on geology, or a biochemist on detailed aspects on an obscure dead language. In general, if someone is quoting someone who has a degree completely irrelevant to the field they are in you can be sure it's an appeal to a false authority. This doesn't mean the authority being appealed to doesn't know anything about the topic however, but it does mean that if they are in blatant contradiction to those who are working in the field they have a good chance of being flat-out wrong.
It's worth noting that there are many times that appealing to an authority is not a logical fallacy. For example, I know my way around immunology, but I know virtually nothing on human neurophysiology. In this case, I wouldn't be incorrect to cite the work and opinions of scientists who are actually neurophysiologists. As with the above, this doesn't automatically make the source right, it just makes them far more credible than someone who has a degree in an irrelevant field for example commenting on the area.
3) Manipulation of statistics: This one is hard to spot unless you know what the answer is ahead of time. It's really common among anti-vaccinists, who love to present the dropping mortality graphs as evidence vaccines do not work. Unfortunately, they rarely present morbidity graphs where the actual number of cases or people being infected only drops after the vaccine has been introduced. The dropping mortality is usually explained by better water sanitation, medical practices and community awareness of that specific disease. Sometimes the statistics are just plain out distorted, as I detailed earlier with Ron Law trying to descredit the MeNZB campaign.
4) Strawmans: A strawman is the indication of the loser in a debate. A strawman is the last resort argument pulled out to try and avoid answering a superior positions arguments and instead distract from the issue at hand. For example, let's say that person A in the debate holds the opinion that when a disaster occurs and hundreds of people are made homeless because of poor water drainage planning, the residents will be extremely angry at the local council. In support of this statement, they note the numerous extremely ticked off people they've seen on the TV as evidence. Person B, who cannot answer the original argument, tries instead to distort it.
Instead of the argument person A gave as being "People I saw on the news were angry because poor planning from the council cost them their homes"
"The statement isn't valid because you don't know if someone wasn't angry and if everyone wasn't angry then it doesn't matter if it was poor planning on the councils part. Therefore people were not angry that their homes were lost."
Now, we can see that this is one mind bending leap of logic. First, they construct a strawman of the original argument, from noting that people person A had seen on the news were angry into everyone being angry in the town as the primary argument. If person A cannot establish everyone as being angry, it automatically refutes the remainder of the statement. This is a strawman, because it's distoring the original position, which never required everyone to be angry and was a simple observation based on the best available evidence person A had seen.
Strawmans are hence a very popular debating tool on the internet as a result as it avoids having to answer the actual argument and supporting evidence put forward.
5) The copy and paster: This is the internet debater I hate the most. Copying and pasting someone elses deficient arguments, aside from being plainly lazy, is just worthless when it's the same crap over and over again. This is very typical of 'minion' creationists, whom in any debate will bombard you with entirely copied and pasted sections of
Copy and pasting large sections of a website is just lazy and demonstrates a lack of knowledge and evidence of the person who is doing it. Sadly, such copy and paste spam is usually very tiring and is one reason that many who try to combat crankery like creationism get very worn out doing it. You are refuting the same things over and over, and many of us have the intellectual honesty to make our own arguments and not just parrot other peoples.
But there you have it in any event, the five top ways to spot when you're arguing with cranks (or people who are just plain clueless).
1. Quote mining
2. Appealing to a false authority
3. Manipulating statistics
4. Strawman arguments
5. The copy and paster