There are 3 versions of translation worth your consideration:
Monkey, by Arthur Waley
(Evergreen Books, 1994)
Arthur Waley's translation of Wu Ch'?ng-?n's original tale was first published in 1942. It is a superb abridgment of the very long original, fast-paced and highly readable, giving a good selection of key episodes focused on the novel's most popular character, the monkey-king known as "Aware-of-Vacuity."
Journey to the West, by Anthony C. Yu
(University of Chicago Press, 4 volumes, 1977-1983)
Professor Anthony Yu stays close to Wu Ch'?ng-?n's original, and is particularly effective in translating the many poems scattered through the text. Even people lacking time to read all four volumes can gain a lot from reading the first volume. This is the first full edition of the work in English.
Journey to the West, by W. J. F. Jenner
(Foreign Languages Press; Reprint edition, 4 volumes, 1984); also available in a one-volume abridged version (Asiapac Books, 1994).
Written fifty years ago by a British translator, it is still very readable, and falls in between Waley and Yu in terms of faithfulness to the original story.
If you want accuracy, look at Anthony C. Yu's four-volume translation, Journey to the West. It includes extensive notes, and is notable for including all the poetry and songs from the original. I linked to the first volume of the revised edition, which uses the Pinyin romanization system instead of Wade Giles and has other updates and revisions.
Anthony Yu's English translation [http://www.actranslation.com/mandarin/mandarin-translation.htm] is the definitive scholarly version, and is definitely the way to go if you're looking for a reference or a crib to read alongside the Chinese text. Waley's translation is dated and abridged (a good thing where Journey to the West is concerned -- the story gets unbelievably repetitive at full length), but is still the most readable one out there.