The following Iftaar duas have been narrated. These duas can be recited after the tasmiyah (Bismillah).
اَللّهُمَّ لَكَ صُمْتُ، وَعَلَى رِزْقِكَ أَفْطَرْتُ
[Abu Dawud, hadith #2358, Al-Adhkar, #494]
Trans: O Allah, for You I have fasted and with Your provision I open my fast.
اَللّهُمَّ لَكَ صُمْنَا، وَعَلَى رِزْقِكَ أَفْطَرْنَا، فَتَقَبَّلْ مِنَّا إِنَّكَ أَنْتَ السَّمِيْعُ الْعَلِيْمُ
Trans: O Allah, for You we have fasted and with Your provision we open our fast, so accept it from us. Indeed, You are the All-Hearing, the All-Knowing.
It has been reported by Sayyiduna Abdullah bin Amr bin ‘Aas that the Messenger of Allah ﷺ said: “When the fasting person opens his fast, his dua is not rejected.”
Ibn Abi Mulaikah said: When Abdullah bin Amr bin ‘Aas opened his fast, I heard him say:
اَللّـهُمَّ اِنّي أَسْأَلُكَ بِرَحْمَتِكَ الَّتِيْ وَسِعَتْ كُلَّ شَيْءٍ أَنْ تَغْفِرَ لِىْ
[Ibn Majah, hadith #1753, Al-Adhkar, #497]
Trans: O Allah, I ask you through Your Mercy that encompasses everything, that You forgive me.
اَلْحَمْدُ للهِ الَّذِيْ أَعَانَنِيْ فَصُمْتُ ، وَ رَزَقَنِيْ فَأَفْطَرْتُ
Trans: All praise belongs to Allah, Who assisted me so I can complete my fast and He has provided for me so I opened my fast.
Sayyiduna Abdullah ibn Umar (Allah is pleased with him) narrates that whenever the Messenger of Allah ﷺ opened his fast, he would say:
ذَهَبَ الظَّمَأُ، وَابْتَلَّتِ الْعُرُوْقُ وَ ثَبَتَ الْأَجْرُ إنْ شَاءَ الله تعالى
[Abu Dawud, hadith #2357, Al-Adhkar, #493]
Trans: The thirst has quenched, and the veins have moistened, and insha’Allah the reward been recorded.
In hadith there is no dua for sehri/suhoor. The Arabic words بصوم غد نويت (bi saumi ghadin nawatu), is the intention to fast. These words are not in hadith, yet there is no harm in reciting it to express one’s intention (niyyah) in Arabic. The regular sunnah duas for before and after meals can be recited for sehri/suhoor.