English Translations of the Quran
Muslims believe that the Quran is the revealed word of God. It happens to be in Arabic. Any translation into another language, like English, can only be an interpretation of the meaning, as is obvious if you compare two or more translations - sometimes they don't say at all the same thing! In general, the translator can attempt to render the text as literally as possible, or he can attempt to capture the meaning and flavor of the text, but not both.
There are a number of translations of the Quran into English. This is not a comprehensive list, but rather a list of several that I recommend, and several that I feel people should avoid.
1) The Meaning of the Glorious Koran, by Mohammad Marmaduke Pickthall. Pickthall was a British convert to Islam in the early 20th century. His translation sticks closely to the Arabic text and to the interpretations made by Muslims. It is also very easy to find and inexpensive. The only drawback is the archaic language (thee and thou and the like), which makes it difficult to read. Nonetheless, this is my preferred translation.
2) The Holy Qur'an: Translation, by Abdullah Yusuf Ali. Available in several versions including with Arabic text, commentary, or Roman transliteration. His translation is looser than Pickthall's but sometimes captures the flavor of the Arabic better. This translation is also widely available in one or another of its versions. Contains some archaic language but not as much as Pickthall.
3) The Koran Interpreted, by A.J. Arberry. This translation is by a non-Muslim. Arberry has really made efforts to render his translation in the most beautiful language and style. However, his rendering of certain passages may differ from that of other translators because he did not make use of Islamic interpretations. Also, the system of verse numbering is different than that of other translations, which makes it difficult to use as a reference.
Translations to Avoid
1) The Noble Qur'an in the English Language, by Muhammad al-Hilali and M.M. Khan. These authors have inserted a lot of commentary in parenthetical notes in the text, and this is why I do not like it. It gives a very misleading idea to non-Muslims or to new Muslims what the Arabic text of the Quran is. If the commentary had been put in footnotes rather than the main body of the text, this would be on my recommended list instead. Use this only if you are familiar with the Arabic text of the Quran and can determine what is commentary and what is the Quran.
2) The Koran, by J.M. Rodwell. This is a translation by a Christian missionary. Not only does this introduce bias into his rendering, but he has also left out several verses at the end of Surah al-Baqarat, and the last four surahs. As such, this translation is really unusable. Avoid it.