Lot 18 is having a contest to see how many friends you can get to signup to their service.

@lot18 win $500 by inviting friends, wine, and other gourmet products.
Invite your friends to Lot18 and receive $25 when their first order ships. There’s no limit to the amount of credit you can earn so blog, tweet, email or share your customizable invite link however you’d like. Invite away and get rewards for spreading the word.