What are some Qur'anic verses regarding forgiveness?

One of the outstanding characteristics of Allah is His mercy and forgiveness. He is the most merciful and the most forgiver. His forgiveness and mercy are mentioned more than 80 times in the Qur’an.

As instances some of these verses are here:

قُلْ يَا عِبَادِيَ الَّذِينَ أَسْرَفُوا عَلَىٰ أَنفُسِهِمْ لَا تَقْنَطُوا مِن رَّحْمَةِ اللَّـهِ ۚ إِنَّ اللَّـهَ يَغْفِرُ الذُّنُوبَ جَمِيعًا ۚإِنَّهُ هُوَ الْغَفُورُ الرَّحِيمُ

Say [that Allah declares,] ‘O My servants who have committed excesses against their own souls, do not despair of the mercy of Allah. Indeed Allah will forgive all sins. Indeed, He is the All-forgiving, the All-merciful. (39:53)

أَ لَمْ يَعْلَمُوا أَنَّ اللَّهَ هُوَ يَقْبَلُ التَّوْبَةَ عَنْ عِبادِهِ وَ يَأْخُذُ الصَّدَقاتِ وَ أَنَّ اللَّهَ هُوَ التَّوَّابُ الرَّحيم

Do they not know that it is Allah who accepts the repentance of His servants and receives the charities, and that it is Allah who is the All-clement, the All-merciful? (9:104)

وَهُوَ الَّذِي يَقْبَلُ التَّوْبَةَ عَنْ عِبَادِهِ وَيَعْفُو عَنِ السَّيِّئَاتِ وَيَعْلَمُ مَا تَفْعَلُونَ

It is He who accepts the repentance of His servants, and excuses their misdeeds and knows what you do. (42:25)

وَمَن يَعْمَلْ سُوءًا أَوْ يَظْلِمْ نَفْسَهُ ثُمَّ يَسْتَغْفِرِ اللَّـهَ يَجِدِ اللَّـهَ غَفُورًا رَّحِيمًا

Whoever commits evil or wrongs himself and then pleads to Allah for forgiveness, will find Allah all-forgiving, all-merciful.(4:110)

For more you can refer to (2:135), (5:9), (2:186), (2:222), (2:221), (2:268), (57:21) and so many other verses.