Economist's conversion process
The Economist has an interesting conversion funnel: non-logged in readers can read 1 ( perhaps 3 ) articles for free, while logged-in readers ( non-paying ) can read up to 6 articles per week. Here's the sign up flow:
Step 1: Alerting readers that they have reached their limit:
Step 2: The Sign Up Form
A short and sweet sign up funnel.