The Open Thread posted at the beginning of the month has gotten really, really big, so I've gone ahead and made another one. Post your new discussions here!
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.
If you mean in general (ie. 'I really liked Evangelion and thought that Sayonara Zetsubou-Sensei was hysterical!'), I think that's a wee bit too far off-topic. Might as well ask what's everyone's favorite poet.
If you mean, 'what anime/manga was most insightful into LW-style thinking and problems', that's a little more challenging.
Death Note comes to mind as a possible exemplar of what humans really can do in the realm of action & thought, and perhaps what an AI in a box could do. Otaku no Video is useful as a cautionary tale about geekdom. And to round it off, I have a personal theory that Aria depicts a post-Singularity sysop scenario with humans who have chosen to live a nostalgic low-tech lifestyle* because that turns out to be la dolce vita.
* The high tech is there when it's really needed. Like how the Amish make full use of modern medicine, surgery, and tech when they need to.
Fullmetal Alchemist Brotherhood has (SPOILER):
an almost literally unboxed unfriendly "AI" as main bad guy. Made by pseudomagical ("alchemy") means, but still.