You've finished your prayer and want to know if there's something specific recommended to say afterward.
What to know
There's a well-known, specific set of remembrance (dhikr) recommended right after each obligatory prayer — it isn't obligatory, but it's a consistently practiced sunnah with real reward attached.
What you can do
Say SubhanAllah 33 times, Alhamdulillah 33 times, and Allahu Akbar 33 times, then complete the 100th by saying 'La ilaha illallah, wahdahu la sharika lah...'
Ayat al-Kursi and the last three surahs (Al-Ikhlas, Al-Falaq, An-Nas) are also commonly recited after each obligatory prayer.
This is recommended, not obligatory — if you're short on time, even a shortened version still carries real reward.