The translation that is the most popular with English-speaking Muslims is the one by A. Yusuf Ali. He put in loads of helpful, informative explanatory footnotes. Tinged with mystical Sufi and Isma`ili perspectives. (Beware: some years ago the fundamentalists got ahold of it and censored all the nice mystical stuff. If the copy you find is published by Amana in Maryland, that’s the censored version. However, Amana’s 1995 printing has a good subject index added.)
Pickthall’s translation was the first by a native English-speaking Muslim. Its language is heavily King James-style, and is not used today as much as it once was.
Muhammad Asad (Leopold Weiss)'s translation is the most intellectual. It also has lots of explanatory footnotes. Some people like this one the best.
Thomas B. Irving is a Canadian Muslim and his translation was designed to be in modern American English for today’s youngsters. Its style is plain & straightforward, but lacks elegance. Irving’s background is in Spanish literature, and in his introductions to the surahs he draws interesting parallels with various kinds of literature.
My personal favorite is the one by Ahmed Ali, mentioned above by our Kyla. His daughter helped him in the preparation of it. So it’s the only one that has a woman’s input. I really* like his interpretation of verse 4:34…
(Nitpicks: I agree with Mjollnir that the spelling Qur’ân is preferable.
The Qur’ân is considered the “uncreated” Word of God, but not identical with God Himself.
The Arabic plural of hadîth is ahâdîth, but in English it’s fine to just write “hadiths.”)