And FreeAMVs, thanks for that last one, I hadn't seen it before, it might do the trick. Radical Yue, thanks for the list, they were pretty much the ones I'd considered up to this point as well
I've caught people singing along with Something Fishy at the few cons I've seen it at... The song is somewhat "audience participation" at one point... I was going to suggest it, but Yue beat me to it.
I've also seen it used as a "guessing game" at Iron Chef competitions.. Have people guess the animes used in it - this sort of thing works for just about any mass multi-anime amv though