As for miracle in the Quran - there is a thread about the splitting of the moon. I've argued in that thread that science can explain how the moon appeared to be split - but that this doesn't lessen the miracle.
The biggest miracle to my mind is the name 'Quran' itself. It means 'that which is to be recited often' - and the Quran, by my estimation, is the most read scripture in the world - ever. It is the most recited revelation of all time. (It does not mean 'book' - but rather recitation - the Quran being a spoken revelation and is meant to be recited - and was preserved by people memorising the revelation word for word).
The opening 7 verses of the Quran are recited over 1 billion times each day (conservatively) - an observant Muslim will recite it at least 30 times a day, for example.
And each year since the revelations came to earth the Quran is recited more and more each year. It is indeed a revelation that is widely recited.
This prophecy in the name was made a millenium and a half ago in the desert of Arabia. God says this is His words and that He will protect it. To this day it is recited in full by millions each year, and with Ramadhan coming up, it will be recited in full from memory by millions in the coming month.
A truly great miracle - and ensures that the God's final testament - and one that Jesus prophecised about in the 'spirit of truth' verse, is preserved for eternity.