More than that, we also rejoice in God through our Lord Jesus Christ, through whom we have now received reconciliation. -Romans 5:11 (ESV)
In addition to rejoicing (boasting) in the hope of the glory of God and in our sufferings as well, we can also rejoice in God himself because Jesus Christ has completed our reconciliation.
As Kruse points out in his commentary, Paul seems to closely link justification and reconciliation. Justification can be seen as the legal (forensic) aspect of our standing, whereas reconciliation speaks of our relational standing with God.
The Christian has much to rejoice in because of Jesus Christ: we have hope in an eternal future with God, we have hope in our sufferings even. But more than that, we can rejoice in our standing and personal relationship with God.