One of the best referral generators I've heard of is simply a delicious fruit basket.
A realtor would send a fruit basket to his client after the close of a successful close of escrow.
Unlike candy, which tends to get hoarded by the recipient, fruit has a built-in expiration date, so people keep it on display to share.
He sends this fruit basket to his client's place of employment, which makes them feel special. When co-workers ask where it came from, the client simply says, "My realtor gave it to me." This opens the door to many subsequent referrals