I've had the Foster book about twenty years now, but mine's becoming so dog-eared, I'm soon going to have to get another copy. It's the first source of information I go to when I need to find something out, after which I am able to use the references to go further. Recently I bought the Complete Tolkien Companion by J. Tyler as well. This latter book I find useful because it covers material from UT and HOME, which unfortunately Foster's guide doesn't.
this robert foster guy must be a J.R.R. Tolkien expert!!!
He is even quoted by Christopher Tolkien in the notes of UT From UT page 284
On the basis of this record Mr Robert Foster says in the Complete Guide to Middle Earth that.....