Unroll.me, a service that helps you unsubscribe from email lists, has data on its 2013 unsubscribers.
Typical mailing list unsubscribe rates are usually around 1%, so these numbers might seem insanely high. But keep in mind this data is just for Unroll.me users, a demographic who signs up for the service specifically to clean out their inbox.
The main takeaway is that the kind of sites that are most unsubscribed from are the kind people typically make one-time purchases. For example, after you send Mother's Day flowers, you don't really want to hear about floral deals the rest of the year, right?