What I think would perhaps be the most authentic translation of the Qur'aan into English, is "Quran-e-Karim: Arabic with English Translation" by Justice Mufti Muhammad Taqi Usmani Saheb. It can be downloaded from here: http://noorehidayat.org/ I don't think Mufti Taqi Saheb needs any introduction, as his in-depth `Ilm of the Deen is widely known. And as he is Deobandi, it is better to read his translation than those of the Salafi Ulama like "The Noble Qur'aan" of Professor Taqi-ud-Deen al-Hilali and Dr. Muhsin Khan, or translations like Yusuf Ali's (Which is filled with errors as was pointed out by Maulana A.S. Desai), or Shakir's, or Pickthall's, despite the fact that the english used by them is of a much higher level that that of Mufti Taqi Usmani.