Here are some of the adhkar that one can say after finishing his Prayer and if you need more you can find many other adhkar in the book of Fiqh Al- Sunnah of Sayed Sabiq.

1- It is reported that, “When the Prophet finishes his prayer, he would seek Allah’s forgiveness three times and then say, ‘O Allah, You are the peace, and from You is peace. You are filled with good, O Sublime and Honorable One.” (Reported by the Group)

2- Then you say as the prophet (peace and blessing be upon him) advised his companion Mu`az ibn Jabal “I advise you, O Mu`az, say at the end of every prayer,  (Allahummah A’inni Ala Dhikrika Wa Shukrika Wa Husni Ibadatika) ‘O Allah, aid me in Your remembrance, Your thanks, and in perfecting Your worship.”  (Ahmad)

3- After that you say as it is reported by ibn Zubair “When the Prophet made the taslim at the end of the prayer, he would say, (La’ilah Illa Allah Wahdahu La sharika Lahu Lahul Mulk walahul Hamd Wahuwa ‘Ala Kulli Shai’in Qadir. La Hawla wala Kuwwata Illah Billah, Wa La Na’budu Illa Iyyah Lahun Ni’matu wa Lahul Fadhl walahuth Thanahul Hasan, La Ilaha Illah Lah, Mukhlisina Lahud Din walaw Karihal Kafirun) ‘There is no god but Allah the One. There is no partner with Him, to Him belongs the sovereignty and to Him is the praise. He has power over all things. There is no might or power save with Allah. We do not worship any but Him. To Him belongs the fortune, the grace and the best praise. There is no god except Allah, and religion is sincerely for Him even if the disbelievers abhor it.” (Ahmad)

4- After finishing these adhkar you can recite the verse of Al-Kursi, since it is narrated by Ali, may Allah be pleased with him, that the Prophet (peace and blessings be upon him) said “Whoever recites the verse of the throne (Ayatul Kursiy) at the end (after) of every obligatory prayer will be in Allah’s protection until the next prayer.” (Al-Tabarani) Also, you can read the surahs of Al-Ikhlas and Al-Mu`awizatayn.

5- At the end, as it is reported by Abu Hurairah that the Prophet (peace and blessings be upon him) said that “Whoever glorifies Allah (Subhanallah) after every prayer thirty-three times, and praises Allah (wal Hamdu Lillah) thirty-three times and extols Allah’s greatness (Wallah Akbar) thirty-three times and then says, ‘There is no god except Allah, the One. There is no partner with Him. His is the dominion and His is the praise, and He has power over all things,’ is forgiven, even if his sins are as abundant as the foam of the sea.