There are a number of translations and commentaries on the I Ching. My favorite is the Richard Wilhelm/Cary F. Baynes translation which includes a forward by C.G. Jung and was first published in 1950. The book begins with a very thorough explanatory introduction by Wilhelm. The body of the book is divided into three parts - the Text, the Material, which is a commentary on the text as a whole, and the Commentaries, which interprets each hexagram in depth. The last two sections are a combination of the writings of ancient scholars and of Wilhelm. From what I understand, the Wilhelm is the standard translation of the I Ching.

A more recent translation is that of Taoist Master Alfred Huang. I am not as familiar with this one, but in some ways it's easier to explore as the text and commentaries are together, rather than in separate parts of the book as in the Wilhelm.