My maths teacher recommended all of the above to me. I started with an arbitrary selection of their books and ended up with most of them. Raymond Smullyan's logic puzzle books are also definitely on my list. A good dictionary of mathematics is one of the best places though. Having a good top-level summary (and just knowing the words you don't know the meaning of) is a great spur to doing your own reading into the subject.

If they work more than half the time I'd be impressed! So far no key cutter in my locale has managed this, even with *the keys themselves* to copy from.