"people look up at the ceiling when they're trying to recall something abstract and down and to the left when they're trying to recall numbers or something more concrete."

Next time I try to sing Green Grows the Rushes O and get stuck I'll try to remember that - head bobbing up and down to get the numbers coodinated with the images...

Shutting the eyes is one memory technique that hasn't been mentioned. Not to be tried if you're trying to rmemebr a song as you are driving along, maybe. But I'm sure that's why so many of us shut the old eyes singing in clubs and so forth.