The Night Blooming Sirius (or Cereus) is a straggly looking plant with a big white, heavily perfumed white flower. They bloom exactly once a year, at night, usually opening up between 9 and 10 pm, for a few hours.
We had five go off last night. Here's a view of one with an added audience member (look closely at the center of the pic, above the bloom). These things have a seriously strong perfume, so we're talkin' Grateful Dead ambiance here.