Two things I find undeniably pleasing: halftone reproductions of old photos (they don't have to be ladies in their underthings, but it helps) and the combination of black and a single color. I'm usually partial to magenta, but designer Derek Vander Griend makes an excellent case here for yellow.
Got a great poster we should consider for Poster of the Week? Send a high-resolution, color .jpg (no more than 1MB) to firstname.lastname@example.org. The event your poster advertises must be at least 10 days in the future in order for us to consider it.