B6 used to make a bigger deal out of interline partnerships (i.e news/web releases) but they have quietly added a few more airlines and they are not listed on the web site.

I found this out running a google search for "JetBlue interlines" after seeing B6 flights become available as connections from JFK-MAN on Thomas Cook Airlines (MT) website. Found an updated B6 policy (available to public) that lists all current interlines as of 8/27

TAP Portugal - already announced as one-way codeshare but not listed
Thomas Cook - already listed Condor (same company so its not surprising)
China Eastern
China Southern
Saudia aka Saudi Arabian Airlines
Ukraine International
Air Serbia

Personally - the Thomas Cook link is important for those who want a Low Cost Link to Europe and do not have Icelandair, Norwegian, or WOW at their home airport.
Thomas Cook has some great fares to MAN and with European LCC's (Easy Jet, Jet2), you can access the whole continent if you are flexible with timings etc.

I'm surprised AirBerlin is not an interline partner yet since their BFF's (Air Serbia and Etihad) are plus they are going daily on BOS-DUS next summer.