Here is a Byzantine prayer of thanksgiving after communion.
I give thanks to you, O Lord my God, for you have not rejected me a sinner, but have made me worthy to share in your sanctifying mysteries. I thank you for having granted that I, unworthy as I am, be a partaker of these pure and heavenly gifts. O Lord and lover of mankind who died and are risen for us, who gave us these dread and life-giving mysteries for the good of our bodies and the sanctification of our souls: make them serve for the healing of my soul and body, that they may set to flight every foe. Enlighten the eyes of my heart; give peace to the powers of my mind; inspire me with a faith in which there is no shame, a sincere love, a deep wisdom and obedience to your Commandments. May they increase in me your divine grace, and make me dwell in your kingdom. Being preserved by them in your holiness, I will remember your love at all times. From now on, I will not live for myself, but for you, my Lord and benefactor. And thus having spent my earthly life in the hope of life without end, I will one day reach eternal rest where the sound of rejoicing never ceases, where the delight of those who look upon the beauty of your face has no bounds. For you are truly the object of our desire and the inexpressible joy of those who love you, Christ our God, and all creatures glorify you forever and ever. Amen.
Some other Byzantine prayers of thanksgiving after communion (courtesy of the Orthodox Christian Foundation @ www.ocf.org):
1. A Prayer of St. Basil the Great
O Master, Christ our God, King of the ages, and maker of all things: I thank thee for all the good things which thou hast bestowed upon me, and for this partaking of thine immaculate and life-giving Mysteries. Wherefore I pray thee, who art good and lovest mankind: Keep me under thy protection, and in the shadow of thy wings; and grant unto me with a pure conscience and even unto my last breath, to partake of thy holy Mysteries, unto remission of sins and unto life everlasting. For thou art the Bread of Life, the Fountain of holiness, the Giver of good things, and unto thee we ascribe Glory: to the Father, and to the Son, and to the Holy Spirit; now and ever, and unto ages of ages. Amen.
2. A Prayer of St. Simeon Metaphrastes
O Thou who willingly dost give thy flesh to me as food, Thou who art a Fire, consuming the unworthy, Consume me not, O my Creator; But rather pass through all my body parts, Into all my joints, my reins, my heart. Burn thou the thorns of all my transgressions, Cleanse my soul, and hallow thou my thoughts. Make firm my knees, and my bones likewise; Enlighten as one my five senses, Establish me wholly in thy fear; Ever shelter me, and guard and keep me From every soul-corrupting deed and word, Chasten me, purify me, and control me; Adorn me, teach me, and enlighten me. Show me to be a Tabernacle of thy Spirit only, And in no wise the dwelling-place of sin, That from me, thy habitation, through the entrance of thy Communion, Every evil deed and every passion may flee as from fire. As intercessors I bring to thee all the Saints, Both the Angelic Leaders of the Bodiless Powers, Thy Fore-runner, and thy wise Apostles; And besides these, thine immaculate and chaste Mother; Do thou accept their prayers, my Christ, who art Compassionate, And make thy servant to be a child of the light: For thou alone, Good Lord, are the sanctification and splendor of our souls, And to thee as God and Master, day by day, Duly we all ascribe glory.
May thy holy Body, O Lord Jesus Christ our God, be unto me for life eternal, and thy precious Blood unto remission of my sins. May this Eucharist be unto me for joy, health, and gladness; and at thy dread Second Coming make me, a sinner, worthy to stand at the right hand of thy glory: through the intercessions of thine all-immaculate Mother and of all thy Saints. Amen.
3. A Prayer to the All-Holy Theotokos
O All-holy Lady Theotokos, light of my darkened soul, my hope, my shelter, my refuge, my consolation and my joy: I thank thee that thou hast accounted me worthy, although unworthy, to be a partaker of the immaculate Body and precious Blood of thy Son. But do thou, who gavest birth to the true Light, enlighten the mental eyes of my heart; O thou who didst bear the fountain of immortality, quicken thou me who lie dead in sin. O compassion-loving Mother of the merciful God, have mercy upon me and grant me humility and contrition of heart, and meekness in my thoughts, and deliverance from the bondage of my vain imaginings. And account me worthy, even unto my last breath, to receive without condemnation the sanctification of the immaculate Mysteries, unto the healing of both soul and body. And grant unto me tears of repentance and confession, that I may hymn thee and glorify thee all the days of my life: for blessed and glorified art thou unto all ages. Amen.
Another Byzantine prayer of thanksgiving after communion (courtesy of Eastern Orthodox Prayers @ prayerbook.riewe.com):
Now lettest Thou Thy servant depart in peace, O Master, according to Thy word: for mine eyes have seen Thy salvation, which Thou hast prepared before the face of all peoples; a light of revelation for the Gentiles, and the glory of Thy people Israel.
Holy God, Holy Mighty, Holy Immortal, have mercy on us. Thrice
Glory to the Father, and to the Son, and to the Holy Spirit, both now and ever, and unto ages of ages. Amen.
O Most Holy Trinity, have mercy on us. O Lord, blot out our sins. O Master, pardon our iniquities. O Holy One, visit and heal our infirmities for Thy name's sake.
Lord, have mercy. (Thrice)
Glory to the Father, and to the Son, and to the Holy Spirit, both now and ever, and unto ages of ages. Amen.
Our Father, who art in the heavens, hallowed be thy Name; thy kingdom come, thy will be done on earth, as it is in heaven. Give us this day our daily bread, and forgive us our debts, as we forgive our debtors; and lead us not into temptation, but deliver us from the Evil One. [For Thine is the kingdomn and the power and the glory of the Father, Son, and Holy Ghost, now and forever and unto the ages of ages. Amen]
(If it is the Liturgy of St. John Chrysostom:
Troparion to St John Chrysostom, Eighth Tone:)
Grace shining forth from thy mouth like a beacon hath illumined the universe, and disclosed to the world treasures of uncovetousness, and shown us the heights of humility; but while instructing by Thy words, O Father John Chrysostom, intercede with the Word, Christ our God, to save our souls.
Glory...
(Kontakion, 6th Tone:)
From the heavens hast thou received divine grace, and by thy lips thou dost teach all to worship the One God in Trinity, O John Chrysostom, all blessed righteous one. Rightly do we acclaim thee, for thou art a teacher revealing things divine.
(But if it is the Liturgy of St. Basil the Great:)
Thy fame hath gone forth into all the earth, which hath received thy word. Thereby thou hast divinely taught the Faith; thou hast made manifest the nature of created things; thou hast made the moral life of men a royal priesthood. O Basil, our righteous father, intercede with Christ God that our souls be saved.
Glory…
Thou didst prove to be an unshakable foundation of the Church, giving to all mortals an inviolate lordship, and sealing it with thy doctrines, O righteous Basil, revealer of heavenly things.
Both now...
O protection of Christians that cannot be put to shame, O Mediation unto the Creator unfailing, disdain not the suppliant voices of sinners; but be thou quick, O good one, to help us who in faith cry unto Thee; hasten to intercession and speed thou to make supplication, thou who dost ever protect, O Theotokos, them that honor thee.
Lord, have mercy. (Twelve times)
Glory to the Father, and to the Son, and to the Holy Spirit, both now and ever, and unto ages of ages. Amen.
More honorable than the Cherubim, and beyond compare more glorious than the Seraphim, who without corruption gavest birth to God the Word, the very Theotokos, thee do we magnify.