As a Scandinavian player, I get this quite often and always play 2. ... c5. Depending on how White continues, I then either play e6 to transpose into a French, which is my second main answer to 1. e4, or Bf5 first to reach an improved French-like position with the bishop out.
I haven't tried 2. ... d4, but I'd guess it's not that great since it seems to weaken the center.
Instead of playing the usual 2)exd5, White tries e5. What, in your opinion, is the best reponse for Black? Is d4 then c5 ok?