"Then Abimelek brought sheep and cattle and male and female slaves and gave them to Abraham, and he returned Sarah his wife to him. And Abimelek said, 'My land is before you; live wherever you like.'" NIV translation
We see that Abimelek went well above what God had required him to do as he presented gifts to Abraham. This man that Abraham had accused of being ungodly was actually showing more honor to God than Abraham had done in not trusting God. His actions remind us that, with repentance, comes a new attitude and that attitude is backed up by action. Abimelek was truly sorry for what he had done and he set about making it right.
"To Sarah he said, 'I am giving your brother a thousand shekels of silver. This is to cover the offense against you before all who are with you; you are completely vindicated.'" NIV translation
Abimelek's repentance included making things right with Sarah. He gave what would have amounted to about 25 pounds of silver for his offence against her. It is interesting to note that he says he gave it to her "brother" reminding them of the fact that their lie started the mess.
"Then Abraham prayed to God, and God healed Abimelek, his wife and his female slaves so they could have children again, for the Lord had kept all the women in Abimelek's household from conceiving because of Abraham's wife Sarah." NIV translation
We see that Abimelek had become cursed because of Abraham's lie. Even though Abraham had lied, God still heard and answered his prayer on behalf of Abimelek. That is a reminder to us, as Christians, that we do not have to be perfect to have God hear and answer our prayers. Abraham, the father of our faith, was not perfect and yet God heard and used him in a mighty way.