I don't have a specific one in mind but I think a great welcome email should be:
- Catchy
- Clean (in terms of layout)
- Not too heavy in content
- Very welcoming - Greeting the user by their first name
- Give a brief introduction of the site we just subscribed to
- Give brief guiding steps for beginners
- Clearly show how the user can best benefit from the site and how it caters to their needs.