Google extant roundhouses. This means only pictures on Google. Like Crestline, things may be different today.
There are two turntables at Schaffer's Crossing.
DM&IR Two Harbors MN. Not used by the railroad.
DM&IR Proctor MN. Actually two of them. The bigger one to the west looks like the turntable is still in use.
Ma & Pa Baltimore MD. Used by Baltimore DOT.
L&NH West Pen Argyl PA.
Sandy River RR Phillips ME. Reconstructed.
Sierra RR Jamestown CA.
Connecticut Eastern Railroad Museum. Reconstructed.
LIRR Morris Park, Jamaica, NY. In use!
Enola PA. Two stalls down from a full circle. In use.
And last but not least the one I work in on occasion.
Steamtown NHS, Scranton PA. Reconstructed.