Pearl's causality stuff and Jaynes' Bayes stuff are probably something a lot of LW readers want to know better. I don't know how ankifiable they are, I have a very poor grasp of either. My impression is that probability math is a bit more loaded with hard to formalize background concepts (cf. Tim Gowers' musings about just what random variables are) than some other fields. This might make a straightforward flashcard approach less useful.
Category theory and abstract algebra seem to start with a bunch of basic definitions which you could memorize with flashcards, but getting anywhere in them even with the definitions handily uploaded in your brain takes quite a bit of mathematical maturity. I tried to do CT with Anki, but got bored quickly since I didn't have any study plan beyond that and am nowhere near the mathematical skill where I could just start doing interesting stuff by myself using the definitions.
Spaced repetition is a powerful learning tactic, and Anki is a good tool for it. There are some LW-relevant Anki decks here. But I wish there were more.
Which sets of knowledge are (1) likely useful to LWers, and (2) straightforward to encode into Anki decks without needing to be familiar with that field?
Some examples:
Which other sets of knowledge would you like to see Ankified? Please link to the actual knowledge set you'd like to see encoded.