That’s actually a tough question because Elizer/others tend to use new names for existing ideas. For example, 'the fallacy of the grey' instead of 'the continuum fallacy', so I am not entirely sure what concepts have been covered elsewhere. Also, I think a lot of the value from less wrong posts comes from them getting you to think about an idea that you may not otherwise have thought to look deeply into even though technically it may have been in the books you have read. For example, I would never have looked into kent berridges work on wanting and liking if I hadn’t read luke prog’s post on it.

The below list contains some of the concepts that I don't think are covered elsewhere. You can also go through the wikis since you should know what topics you have already learnt:

• Friendly artificial intelligence – is a superintelligence (i.e., a really powerful optimization process) that produces good, beneficial outcomes rather than harmful ones.
• Decision Theories – Theories invented by researchers associated with MIRI and LW: TDT, Timeless Decision Theory, UDT, Updateless Decision Theory and ADT: Ambient Decision Theory (a variant of UDT)
• Affective death spiral - positive attributes of a theory, person, or organization combine with the Halo effect in a feedback loop, resulting in the subject of the affective death spiral being held in higher and higher regard.
• Chronophone – is a parable that is meant to convey the idea that it’s really hard to get somewhere when you don't already know your destination. If there were some simple cognitive policy you could follow to spark moral and technological revolutions, without your home culture having advance knowledge of the destination, you could execute that cognitive policy today.
• Free will (explanation) - means our algorithm's ability to determine our actions. People often get confused over free will because they picture themselves as being restrained rather than part of physics. Yudowsky calls this view Requiredism, but most people just view this essentially as Compatibilism.
• Politics is the Mind-Killer – Politics is not a good area for rational debate. It is often about status and power plays where arguments are soldiers rather than tools to get closer to the truth.
• The map is not the territory – the idea that our perception of the world is being generated by our brain and can be considered as a 'map' of reality written in neural patterns. Reality exists outside our mind but we can construct models of this 'territory' based on what we glimpse through our senses.
• Probability is in the Mind - Probabilities express uncertainty, and it is only agents who can be uncertain. A blank map does not correspond to a blank territory. Ignorance is in the mind.
• Adaptation executors - Individual organisms are best thought of as adaptation-executers rather than as fitness-maximizers. Our taste buds do not find lettuce delicious and cheeseburgers distasteful once we are fed a diet too high in calories and too low in micronutrients. Tastebuds are adapted to an ancestral environment in which calories, not micronutrients, were the limiting factor. Evolution operates on too slow a timescale to re-adapt to adapt to a new conditions (such as a diet).
• Cached thought – is an answer that was arrived at by recalling a previously-computed conclusion, rather than performing the reasoning from scratch.
• Applause light - is an empty statement which evokes positive affect without providing new information
• Belief as attire – is a example of an improper belief promoted by identification with a group or other signaling concerns, not by how well it reflects the territory.
• Belief as cheering - People can bind themselves as a group by believing "crazy" things together. Then among outsiders they could show the same pride in their crazy belief as they would show wearing "crazy" group clothes among outsiders. The belief is more like a banner saying "GO BLUES". It isn't a statement of fact, or an attempt to persuade; it doesn't have to be convincing—it's a cheer.
• Belief in belief I believe this is dennet’s idea - Where it is difficult to believe a thing, it is often much easier to believe that you ought to believe it. Were you to really believe and not just believe in belief, the consequences of error would be much more severe. When someone makes up excuses in advance, it would seem to require that belief, and belief in belief, have become unsynchronized.
• Counter man syndrome - wherein a person behind a counter comes to believe that they know things they don't know, because, after all, they're the person behind the counter. So they can't just answer a question with "I don't know"... and thus they make something up, without really paying attention to the fact that they're making it up. Pretty soon, they don't know the difference between the facts and their made up stories
• Crisis of faith - a combined technique for recognizing and eradicating the whole systems of mutually-supporting false beliefs. The technique involves systematic application of introspection, with the express intent to check the reliability of beliefs independently of the other beliefs that support them in the mind. The technique might be useful for the victims of affective death spirals, or any other systematic confusions, especially those supported by anti-epistemology.
• Making Beliefs Pay Rent - Every question of belief should flow from a question of anticipation, and that question of anticipation should be the centre of the inquiry. Every guess of belief should begin by flowing to a specific guess of anticipation, and should continue to pay rent in future anticipations. If a belief turns deadbeat, evict it.
• Least convenient possible world – is a technique for enforcing intellectual honesty, to be used when arguing against an idea. The essence of the technique is to assume that all the specific details will align with the idea against which you are arguing, i.e. to consider the idea in the context of a least convenient possible world, where every circumstance is colluding against your objections and counterarguments. This approach ensures that your objections are strong enough, running minimal risk of being rationalizations for your position.
• Rationalist taboo - a technique for fighting muddles in discussions. By prohibiting the use of a certain word and all the words synonymous to it, people are forced to elucidate the specific contextual meaning they want to express, thus removing ambiguity otherwise present in a single word. Mainstream philosophy has a parallel procedure called "unpacking" where doubtful terms need to be expanded out.
• Semantic stopsign – is a meaningless generic explanation that creates an illusion of giving an answer, without actually explaining anything.