Countdown Timer on http://justfab.com. In this instance, the stated offer is valid even after the hour long timer expires.
The user can unknowingly sign up for a membership to the site when they purchase something unless they read the fine print in the terms and conditions
A presentation by Harry Brignull on Dark Patterns. Includes examples from Apple, Post-office.co.uk, Royal Mail, Santander, Quora, Twitter, The Ladders, JustFab, Next.co.uk and M&S.