Have any of the major actors read the books (before actually filming)?

I know for sure that Christopher Lee has read it....and more than once. I believe he said he has read it once a year since he first read it a long time ago. I also know that Billy Boyd's read it. He read it when he was twelve or so and that's why he tried out for the part of Pippin. Viggo hadn't read it when he was asked to play the part of Aragorn, but like Dearheart said, his son was a huge fan. I think that Ian McKellen hadn't read it at all when the movies were made, but don't quote me on that.

It's possible David Wenham has, though I'm not completely sure. I know for a fact that Viggo Mortensen began reading The Lord of the Rings on the way to New Zealand...and his son, Henry, was a HUGE Tolkien fan. Aragorn was a favorite book hero to him, which is a big part of how he convinced his dad to take the role.

The picture below is a screencap from The Two Towers (I don't remember if it's an extended scene or not). On the left is Viggo, and the boy on the right is Henry, who got a cameo. It's a small but wonderful scene between the two of them, both as LotR characters and as father and son. :-)

In a documentary on the first special features disk on special addition, it said that all the actors read it many times while filming to know exactly what they were supposed to do.

I'm Pretty Sure David Wenham has. He said he did at one of the permiers.

I heard that Ian McCleland has read it

I know that chris lee reads them once a year or so he says and why lie.as for the otheres who knows.I've read all the books including the hobbit.they are a hard read but well worth it.

Yes, if you have the extended cut dvd's and watch some of the Special Features some of the actors admit reading the book and wanting to make a film.

I'm sure most of them read it because it would obviously really help them, Christopher Lee says on the special features (or someone else says it) that he reads it every year,

yes