any recommendation for a good excel VBA reference book?

I am new to excel VBA, but not that new. From time
to time, I learn some good/fancy vba command by
looking at someone else's code. This is a way of learning
but not a very efficient way of learning. I want to
go through a book to have a better picture of what
are out there in the excel VBA world. Can anyone
refer a good book? Thanks!