• Everything from Paul Christiano's Rational Altruist
• Everything from Carl Shulman's Reflective Disequilibrium
• Selected posts by Greg Lewis, Katja Grace, Brian Tomasik, Lukas Gloor, Holly Elmore, Ben Garfinkel, Jeff Kaufman, Robin Hanson, Julia Wise, and others. I make some concrete suggestions here, but it may also be worth going through their blogs and checking the posts one by one.
• (I'm sure I'm forgetting many other blogs I should recommend but these are the ones that immediately come to mind.)

tl;dr Maybe these cross-posts should initially show up on the front-page, like regular new posts do? (And I'm guessing they currently aren't, since I haven't spotted any.)

Glad to hear this is being done! As I mentioned here, this seems like a good thing to do, because:

• As you mention, "This makes [the content] easier to find via search/tagging, allows people to make comments, lets it be added to sequences, etc."
• If the post pops up on the front page (or somewhere like that), that'd make more EAs aware that it exists (which is good if the post is indeed worth their attention)
• Upvotes, downvotes, and comments on a post could make it easier for people to decide whether reading that post worth their time

But some of these benefits essentially require, or are increased if, the post starts off on the front page (or somewhere like that). 

One not-super-obvious way this can be true is that, while people can make comments on a post that's not on the front page, such comments are likely to have far fewer readers than comments on posts that are currently on the front page. So people have less incentive to comment, and interesting comments reach fewer people.

For example, I recently made a cross-post for a GPI paper, partly to draw attention to it and partly because I'd written a bunch of thoughts on it which I wanted to share as comments. Since this started out on the front page, the post and comments got some attention and responses. This wouldn't have happened if instead I'd commented on an "archive" cross-post - people wouldn't only seen the post or comments if they found it via the tag, searching, or looking at "new comments" on the Forum. 

(In fact, I do have a bunch of notes on another GPI paper that I want to share, but the paper was already cross-posted, so I'm not sure whether to comment there - expecting few readers of the comments - or make a new, separate cross-post or commentary post.)

So maybe these cross-posts should initially show up on the front-page?

Of course, these cross-posts showing up on the front page initially might be bad if there's a large amount of such cross-posts being made per week, since it displaces attention from newer content and might discourage people from posting newer things (if they expect fewer readers). On the other hand, I'm not sure that if that's bad:

• Most of those older, deliberately chosen posts may indeed be more worth people reading than the median new post.
• And people can still be informed about what to read based on upvotes, downvotes, comments, and tags, as usual.
  • If few Forum users think a cross-post is worth people's time, it might just get a comment to that effect, few upvotes, or some downvotes, and thus slip off the radar quickly.

• Some stuff from Paul Christiano's 'The sideways view'

In addition to everything that Pablo said (esp. the Tomasik stuff because AFAICT none of his stuff is on the forum?)

Pretty much all papers and blog posts from the GCRI site (except that some blog posts just discuss a single paper, in which case there should just be one cross-post covering both).

Pretty much all papers, technical reports, etc. from FHI (including GovAI), maybe starting with the Bostrom stuff.