How to Memorize a Random 60-Bit String [pdf]
isi.edu
isi.edu
http://www.washingtonpost.com/news/wonkblog/wp/2015/10/22/th...
I've found that it's easy to memorize 20+ random character passwords if you use them everyday, and I've always had quite a poor memory.
I think the simplest method (IMO) is to pick a dictionary of 100k common but not too common 3+ char words that have realistic memorable structures like adjective -> noun -> verb or adjective -> adjective -> noun or having probabilities that the bigrams are together in google bigrams being nonzero.
and let people veto the combinations a few times.