I just finished reading Moonwalking with Einstein, a journalistic piece on the World Memory Championships. The book explicates the various techniques used by participants to memorize different types of contest materials-- for example, there are techniques for memorizing large lists of numbers, foreign language vocabulary, packs of cards, and poetry.
The Dominic System, for example, is often used for memorizing numbers, the PAO system is often used for memorizing for packs of cards, etc.
However, a lot of these techniques have not been rigorously tested in a scientific setting to determine which forms of techniques are empirically optimal. Often, they're just circulated in underground communities, without any objective way to adjudicate between the merits of competing systems.
I was wondering what the research on memory suggests is the best way to memorize the above types of content. I suppose you need a metric to qualify "the best way", so let's say that preference is given to speed over duration of memory. I'm in the process of learning a new language, so I'm also particularly interested in foreign language techniques.