(from the 1979 Book of Common Prayer – this page with all the readings can be found here)
Almighty and everlasting God, you hate nothing you have made and forgive the sins of all who are penitent: Create and make in us new and contrite hearts, that we, worthily lamenting our sins and acknowledging our wretchedness, may obtain of you, the God of all mercy, perfect remission and forgiveness; through Jesus Christ our Lord, who lives and reigns with you and the Holy Spirit, one God, for ever and ever. Amen.
There is also this prayer during the Ash Wednesday service:
Almighty God, you have created me out of the dust of the earth: Grant that these ashes may be to me a sign of my mortality and penitence, that I may remember that it is only by your gracious gift that we are given everlasting life; through Jesus Christ my Savior. Amen