As Stephen Harris and Wyck point out, I agree that Q&A Highlights is a given.
Expanding on it, the librarian in me would be interested in Editorializing the Archives.
Like a "Tag research", say an article mashing up Theme Development.
Something in the lines of this answer I wrote: Looking for WordPress System Diagrams.
Or this great post Andrea_r G+ the other day: How to do damn near anything with WordPress
Comment of the Day: there's a meta somewhere about this... So many gems we met in the comments threads getting lost in the dustbins of memory, it's not fair!
WPSE Plugin Repository: The plugins that came out of WP-Answers... Also, many little gems floating around that didn't make into that wiki. And could morph into a category, a post series or a page or something more live.
