Jahannam (Hellfire) exists now
Many of the Imams of the Sunnah used this Ayah to prove that the Fire exists now. This is because Allah said,
(prepared) meaning, prepared and kept. There are many Hadiths on this subject. For instance, the Prophet said,
«تَحَاجَّتِ الْجَنَّةُ وَالنَّار»
(Paradise and the Fire had an argument..)
Also, the Prophet said,
«اسْتَأْذَنَتِ النَّارُ رَبَّهَا فَقَالَتْ: رَبِّ أَكَلَ بَعضِي بَعْضًا فَأذِنَ لَهَا بِنَفَسَيْنِ: نَفَسٍ فِي الشِّتَاءِ وَنَفَسٍ فِي الصَّيْف»
(The Fire sought the permission of her Lord. She said, 'O my Lord! Some parts of me consumed the other parts.' And Allah allowed her two periods to exhale, one in winter and one in summer.)
Also, there is a Hadith recorded from Ibn Mas`ud that the Companions heard the sound of a falling object. When they asked about it, the Messenger of Allah said,
«هَذَا حَجَرٌ أُلْقِيَ بِهِ مِنْ شَفِيرِ جَهَنَّمَ مُنْذُ سَبْعِينَ سَنَةً، الْآنَ وَصَلَ إِلى قَعْرِهَا»
(This is a stone that was thrown from the top of Jahannam seventy years ago, but only now reached its bottom.) This Hadith is in Sahih Muslim.
There are many Hadiths that are Mutawatir (narrated by many different chains of narrations) on this subject, such as the Hadiths about the eclipse prayer, the night of Isra' etc.
[فَأْتُواْ بِسُورَةٍ مِّن مِّثْلِهِ]
(Then produce a Surah (chapter) of the like thereof) (2:23), and,
(A Surah (chapter) like it) (10:38) this includes the short and long Surahs of the Qur'an. Therefore, the challenge to creation stands with regards to both the long and short Surahs, and there is no disagreement that I know of on this fact between the scholars of old and new. Before he became Muslim, `Amr bin Al-`As met Musaylimah the Liar who asked him, "What has recently been revealed to your fellow (meaning Muhammad ) in Makkah'' `Amr said, "A short, yet eloquent Surah.'' He asked, "What is it'' He said,
[وَالْعَصْرِ - إِنَّ الإِنسَـنَ لَفِى خُسْرٍ ]
(By Al-`Asr (the time). Verily, man is in loss,) (103:1-2)
Musaylimah thought for a while and said, "A similar Surah was also revealed to me.'' `Amr asked, "What is it'' He said, "O Wabr, O Wabr (i.e. a wild cat), you are but two ears and a chest, and the rest of you is unworthy and thin.'' `Amr said, "By Allah! You know that I know that you are lying.''
[وَبَشِّرِ الَّذِينَ ءَامَنُواْ وَعَمِلُواْ الصَّـلِحَاتِ أَنَّ لَهُمْ جَنَّـتٍ تَجْرِى مِن تَحْتِهَا الأَنْهَـرُ كُلَّمَا رُزِقُواْ مِنْهَا مِن ثَمَرَةٍ رِّزْقاً قَالُواْ هَـذَا الَّذِى رُزِقْنَا مِن قَبْلُ وَأُتُواْ بِهِ مُتَشَـبِهاً وَلَهُمْ فِيهَآ أَزْوَجٌ مُّطَهَّرَةٌ وَهُمْ فِيهَا خَـلِدُونَ ]
(25. And give glad tidings to those who believe and do righteous good deeds, that for them will be Gardens under which rivers flow (Paradise). Every time they will be provided with a fruit therefrom, they will say: "This is what we were provided with before,'' and they will be given things in resemblance (i.e. in the same form but different in taste) and they shall have therein Azwajun Mutahharatun (purified mates or wives), and they will abide therein forever.)