Here are all the LW comments I have bookmarked at del.icio.us/porejide, aside from the one I took from Grognor below. This is probably overkill for a single comment.

1) This comment by Mitchell Porter, for the idea of looking into the time before there was algebra, seeing how it was invented, and using that as an outside view for our current difficult problems (like consciousness).

2) This comment by Eliezer, which I found interesting because it responded to a critique of Bayes Cosmo Shalizi which I also found persuasive, leaving me in a (typical) state of not knowing what to believe.

3) Yvain's comment preceding his post on slippery slopes and Schelling points; this was useful for my thinking about both of those topics.

4) PO8's comment about early detection of cancer and whether the purported benefits could be a selection bias. This is an interesting idea and I intend to look into it further when I get more time.

5) Luke M's comment that the best way to convert someone is to be cool, likeable, and generally sarcastic about the idea you want them to change. Makes sense -- most do not respond well to wordy arguments.

6) Vladimir M's comment that non-mathy pop-physics is unlikely to lead to real insight. I tentatively agree but would like to see some actual data.

7) Carl Shulman's comment on how a normal prior distribution for charity effectiveness does not map well to reality. This doubles as a demonstration of how difficult Bayesian computations can be and an interesting quantitative look at charity.

8) Yvain's comment, which I feel bad re-posting because it is ironic and I'm growing increasingly annoyed with irony, but I include for completeness and because it makes a useful point through its irony.

9) Eugine Nier's comment that it's more important for your beliefs to be correct than consistent. He also gives an example of a situation in which there can be a trade-off between the two. I found this useful because I often am biased towards consistency. I made an Anki flashcard based on this comment.

10) jimrandomh's comment that "drugs" are not a natural category. Useful on both the object (people talk about "drugs" often) and meta (people talk about non-natural categories as if they were natural categories often) levels.

11) komponisto's comment that "I said I was apathetic. I didn't say I was ignorant." I just thought this was clever. Doesn't seem as good in hindsight. But maybe I'm biased by the relatively low upvotes.

12) Nominull's comment that "When promoting the truth, if you value the truth, it is wise to use especially those methods that rely on the truth being true. That way, if you have accidentally misidentified the truth, there is an automatic safety valve." I also made an Anki flashcard for this one.

13) Xachariah's comment deconstructing the phrase "how are you" in a way I still often think about when I hear that phrase.

14) Richard Kennaway's comment discussing the trade-offs to engaging in sexual relationships (i.e., lost time and energy for intellectual pursuits).

15) Konkvistador's comment quoting Peter Thiel saying that as soon as you starting discussing why something occurs, people start losing sight of whether it occurs. Useful rhetorically, depending on your goals.

16) Mitchell Porter's comment about how LW tropes might eventually find political expression, and what that would actually look like. This comment is truly a gem. "Look, politics isn't a game of hide and seek. Ideological groups have the cohesion that they do because membership in the group depends on openly espousing the ideology." I also made an Anki flashcard for this. This kind of comment makes me a bit sad that he appears to be spending much of his time on looking for the quantum correlates of consciousness, which does not make much sense to me. But from the perspective of "fund people, not projects", we should give him leeway.

17) Mitchell Porter's comment dismissing the idea of game theoretic equilibria between intelligences in disjoint worlds. I remember finding it profound when I read it.

18) taw's comment which contains an interesting history lesson on infanticide.

19) Eliezer's comment that you should deal with sunk costs by imagining that you were teleported into someone's life and thinking about what you would do differently if that were the case.

20) Mitchell Porter's comment speculating on what LW's role in history would be. Another gem. Not only was this informative, but I hadn't even thought on that kind of level before.

21) Will Newsome's comment. I forget why I tagged this, but looking back it has some very interesting bits about theism.

22) hegimonicon's comment that there is an "enormous gulf between finding out things on your own and being directed to them by a peer." It's somewhat counter-intuitive that in many cases your best way to convince someone of something is to suggest general lines of reasoning and let them figure out the specifics for themselves.

I hesitate to say this because I don't want to make her embarrassed or change her behavior too much... but whenever Nancy Lebovitz comments, especially when she recommends something to read, I pay attention. It is usually something that (1) I've never seen or heard before and (2) gives useful insight into things from common experience. From the perspective of Aumann updating (which should theoretically happen most productively with people who are well calibrated but have seen different stuff than you have) her posts are almost pure gold to me, and I keep thinking I should PM her and maybe try to figure out some way to spend N days or weeks talking about random subjects with her to get her thoughts on them. Given the constraints of time and resources (busy lives, opposite coasts, etc, etc) all I can say for certain is I'm happy that she's here and that her apropos comments are part of my informational environment on a semi-regular basis :-)

For reference, and because it seems right to mention, she has a blog called Input Junkie and an online button and bumper sticker business.

Above, I linked to her comment feed because it is interesting how regularly I am rewarded by tracking down things she refers to, but when I tried to think of something she linked to that still particularly stands out from ~15 months of distance as having caused cascading re-arrangements in my thinking it would be her comment referencing science fiction as appealing to the fantasy of political agency.

This comment in which gwern describes a 'hope function' - how, given a diffuse prediction of an event with known overall confidence, the confidence should change as specific opportunities for the event fail to occur.