It seems like every year there are new elements coming out, though some do seem to retire every so often.
I recently came across a 4 x 4 corner brick in a bulk lot I picked up at a garage sale. A little research tells me that this particular part hasn't been used in a set since the 60s.
That piece looks really useful.
Doesn't it just? Really hard to believe it hasn't been issued in a set since 1969
That piece in gray, black and brown would be gray for building mountains.