Back in my youth when I used to practice coin magic, the thing to get was an English Penny. It was about the same same as a U.S. half dollar, and there were several fun effects that used the two. As I recall, there was also a brass Chinese coin (I don't recall the name) that had a hole in the center and was also that same approximate size, so again used to make delightful surprises. There were a few things you could do with a U.S. penny and a dime, but the size constraint made them difficult to see, of course.