How do I configure addresses so that they're always displayed in lowercase?

You can configure the case type of an address field for each country.

Here’s how you do it:

1. Sign-in as a setup user.
2. In Setup and Maintenance, click the Tasks icon, then click Search.
3. Search and select Manage Address Formats.
4. Search for a country and click the postal address format of that country. For example, search United States and click United States Postal Address Format.
5. Click Edit and clear the selection checkboxes in the Uppercase column of address fields that must be displayed in lowercase.
6. Save your work.