This one is all about sin, and is about David's sin in sleeping with Bathsheba. I am particularly drawn to verses 10-12.
Psa 51:1 To the chief Musician, A Psalm of David, when Nathan the prophet came unto him, after he had gone in to Bathsheba. Have mercy upon me, O God, according to thy lovingkindness: according unto the multitude of thy tender mercies blot out my transgressions.
Psa 51:2 Wash me throughly from mine iniquity, and cleanse me from my sin.
Psa 51:3 For I acknowledge my transgressions: and my sin is ever before me.
Psa 51:4 Against thee, thee only, have I sinned, and done this evil in thy sight: that thou mightest be justified when thou speakest, and be clear when thou judgest.
Psa 51:5 Behold, I was shapen in iniquity; and in sin did my mother conceive me.
Psa 51:6 Behold, thou desirest truth in the inward parts: and in the hidden part thou shalt make me to know wisdom.
Psa 51:7 Purge me with hyssop, and I shall be clean: wash me, and I shall be whiter than snow.
Psa 51:8 Make me to hear joy and gladness; that the bones which thou hast broken may rejoice.
Psa 51:9 Hide thy face from my sins, and blot out all mine iniquities.
Psa 51:10 Create in me a clean heart, O God; and renew a right spirit within me.
Psa 51:11 Cast me not away from thy presence; and take not thy holy spirit from me.
Psa 51:12 Restore unto me the joy of thy salvation; and uphold me with thy free spirit.
Psa 51:13 Then will I teach transgressors thy ways; and sinners shall be converted unto thee.
Psa 51:14 Deliver me from bloodguiltiness, O God, thou God of my salvation: and my tongue shall sing aloud of thy righteousness.
Psa 51:15 O Lord, open thou my lips; and my mouth shall shew forth thy praise.
Psa 51:16 For thou desirest not sacrifice; else would I give it: thou delightest not in burnt offering.
Psa 51:17 The sacrifices of God are a broken spirit: a broken and a contrite heart, O God, thou wilt not despise.
Psa 51:18 Do good in thy good pleasure unto Zion: build thou the walls of Jerusalem.
Psa 51:19 Then shalt thou be pleased with the sacrifices of righteousness, with burnt offering and whole burnt offering: then shall they offer bullocks upon thine altar.