I'm surprised more people haven't voted this up since I've never seen any system without an Address Line 2. Like others have said, apartments, suites, etc. are common on seconds lines. thank you.

I also need this function to integrate with other direct mail services. Not as a custom value it should be a standard on the General Information AND Very Easily Done.

Here a link to the United States Postal Service on the standard, https://pe.usps.com/text/pub28/28c2_003.htm. Section 213.3, entitled Alternate Location, explains the need and location of a secondary address line. I have personally run into this case where the primary address line is so long, there is not enough room left for a suite number at the end.

Definitely needs to be added on every address form throughout the site. It should not be a required field though. Just stating the obvious there.

As a standard field, not a custom field.