How do I add additional email addresses for eCommerce order notifications?

When an eCommerce order is placed, I would like the email that notifies us to go to a different person.

Where can I change that email?

To do this, you'll want to create additional Squarespace "Contributors" as per this article: http://help.squarespace.com/guides/adding-and-managing-contributors

Each user you create will be associated with the email address you used during signup.

If you assign the proper contributor permissions these accounts will receive Commerce notifications by default (I think). If not, just login to that user account and turn on the notifications as per this article: http://help.squarespace.com/guides/how-do-i-enable-email-comment-notifications

Here's an updated answer on how to add contributors for anyone looking in 2017: https://support.squarespace.com/hc/en-us/articles/206537287