Adoption is certainly one of my favorite NT salvation terms. In the New Testament, God has left us with an abudance of salvation pictures. Reconciliation pictures two parties at war who become friends (Eph 2). Justification pictures God's legal declaration at the Judge's bench (Rom 3-4). Redemption pictures us being purchased at the slave market and set free (Eph 1:7-8). I don't believe adoption get as much press as the other terms. Adoption is a beautiful, warm, word that pictures us being estranged from the father and the family. God sets His love upon us and brings us into the family. He purposed this from eternity past (Eph 1:5-6). This adopting love is something that Christians should consider and imitate their father in heaven.
Check out Albert Mohler's recent post on adoption.