Great post, thanks! In these primitive times without knowledge pills, discussion of methods to improve our learning are very welcome. Here are some I know;

• I found the SuperMemo discussed in this article pretty good for things like learning foreign words (I'm trying to pick up some Finnish vocabulary); I'm not sure how it would work for knowledge that cannot be so easily represented as A=B. I haven't fully explored the potential though.
• My personal favorite are audiobooks; it's a great way to pick up a lot of qualitative knowledge (say, history or psychology), or 'reading' a lot of 19th-century literature. Librivox and friends are excellent resources for that. The great thing about audio books is that I can do something useful with my idle time (shopping, running, commuting etc)
• For language learning, the Pimsleur is an interesting way; it's about repeating simple phrases again and again - completely ignoring writing or grammar, but still a relatively quick way to be able to converse with locals (worked for me with Greek at least to some extent)
• Memorization of random lists of things, like the ones mentioned in Mind Performance Hacks
• Remembering the things to do; GTD and OrgMode are my main tools here.

Still, there is a whole universe of knowledge that cannot be acquired using such tools -- procedural knowledge, deeply technical knowledge. I suppose there is no alternative to sitting down and excercise those gray cells; still, I'd be very interested if anyone has some new approaches there.