The very simple ideas, perhaps? I'm talking about simple on the level of:
These seem assumed by EY's sequences, but I can't find something that specifically asserts and explains them.
(Edit: Tetronian notes that The Lens That Sees Its Flaws covers this idea.)
And these points do need expressly asserting and explaining, because surprising people with these two notions and getting people to notice their minds for the first time is a lot of how nasty memetic infections get to people. (I'm thinking specifically of Scientology, and watching this happen to someone, but if they can do it then lesser but still nasty infections can do the same.)
I suppose "how do I know what I know?" and "why do I believe what I believe?" are about this low level.
This idea is discussed pretty early on in the Sequences; I always found that post to be one of the most compelling.
That essay strikes me as asserting that people can improve their thinking, but having very little detail about how, or about the process of getting over the psychological hump for those who are committed to the impossibility of improving their thinking rather than just ignorant of it.
Those are very important ideas, though I think it's possible to go somewhat farther. Conveying the idea that updating is important, and that it's valuable to appreciate it when people update instead of mocking them for having been wrong, for example.
Taking five minutes to think also seems like a sufficiently simple idea.
Now that I can see it (earlier, your link signaled down for everyone), I can tell that it doesn't have contact information.
Here's the easy idea-- how about a brochure about LW and SIAI? I was just at a couple of science fiction conventions, and it occurred to me that if there were a brochure, I could have printed it out and put it on the freebie table.
The hard idea is Sesame Street for rationalism-- entertaining video that dramatizes rationality. This would require money and possibly talents which aren't currently in the community, but I think a good bit of rationality could be dramatized, and it would be a big win for raising the rationality waterline.