I highly recommend Matthew Henry's commentary. Probably to start with you may want the "concise" version (one book)... but if you really want to go deep deep deep, get the complete version (multiple volumes).
The set that I have is great. Got it for $40 on Ebay. I think there are 8 books total. It starts w/ Genesis 1:1 and ends with Revelation, and the way it is set up is it will have a passage of scripture, and then 2 pages of Henry's observations, comments and teachings on that passage. So you can read it straight thru just like a Bible. And there is so much meat to it.
It was written 300 years ago, but is amazingly simplistic in it's writing so you wont really have any trouble understanding it. There is a real warmth to the way he wrote... kinda makes you feel like you're sitting by a warm fire 300 years ago learning at the feet of this gifted Bible teacher.
This is from Wikipedia:
[i]"Matthew Henry (October 18, 1662 June 22, 1714), was an English nonconformist clergyman.
"He was born at Broad Oak, a farmhouse on the borders of Flintshire and Shropshire. His father, Philip Henry, had just been ejected by the Act of Uniformity. Unlike most of his fellow-sufferers, Philip possessed some private means, and was thus able to give his son a good education. Matthew went first to a school at Islington, and then to Gray's Inn. He soon gave up his legal studies for theology, and in 1687 became minister of a Presbyterian congregation at Chester, removing in 1712 to Mare Street, Hackney. Two years later (June 22, 1714), he died suddenly of apoplexy at Nantwich while on a journey from Chester to London.
"Henry's well-known Exposition of the Old and New Testaments (1708-1710) is a commentary of a practical and devotional rather than of a critical kind, covering the whole of the Old Testament, and the Gospels and Acts in the New Testament. After the author's death, the work was finished by a number of ministers, and edited by G Burder and John Hughes in 1811. Of no value as criticism, its unfailing good sense, its discriminating thought, its high moral tone, its simple piety and its practical application, combined with the well-sustained flow of its racy English style, made it one of the best works of its type."[/i]
I think the Matthew Henry Commentary is the most respected commentary there is. And it truly has stood the test of time. I use it every single day.
Henry obviously used the KJV (which makes me very happy!), and so I recommend it also for those who claim to have difficulty reading and understanding the KJV.
Hope that helps!