This list of 50 Scientifically Proven Ways to Be Persuasive is pretty awesome. Two of my favorites:
2. Introduce herd effect in highly personalized form. The hotel sign in the bathroom informed the guests that many prior guests chose to be environmentally friendly by recycling their towels. However, when the message mentioned that majority of the guests who stayed in this specific room chose to be more environmentally conscious and reused their towels, towel recycling jumped 33%, even though the message was largely the same.
40. Incentive programs need a good start. A car-wash place gave one group of customers a free car wash after 8 washes, and everybody got their first stamp after their visit. Group B got a free car wash after 10 car washes, with 3 stamps on the card. Both groups needed to make 7 more trips to get a free wash. 19% of the Group A returned, while 34% of the Group B did.
These are all taken from a book of the same name. (via lone gunman)