The KJV is only the most authoritative English translation for some sects. It's not regarded as the most accurate translation (in part because older manuscripts have been discovered since the KJV was produced). It is also not the most readable since the English language has changed since the 17th Century - a fact which also sometimes leads to misunderstandings.
The version that I have usually seen recommended is the New American Standard Bible (NASB) - which is perhaps a little less easy to read than the New International Version (NIV) but doesn't have the omissions and questionable readings of the NIV.
BibleGateway.com: A searchable online Bible in over 150 versions and 50 languages. has the "Bible Gateway" which features several translations on line including the KJV, NASB and NIV.