I don't actually tell my students what to call me, and I get a whole mix of "Dave," "Mr. Slaven," "Dr. Slaven," and just "Slaven." I once had a student tell me I looked just like his dad, and he started calling me "Dad," but I drew the line there. :-)
It probably varies some from place to place. I teach at a small college of about 1200-1300 students.
When I was a student, I mostly called my professors by "Dr." (assuming they had a Ph.D.) But of course, this was a long time ago. (The 80's.)
"It's only Neutron. We call him that because he's so positive." --from This Island Earth