Polygon Counter Plus
A script tool for counting the polygons/tris in the scene and on the selected objects. But wait! It does so much more. Tells you how many objects/helpers/lights/cameras/splines are in the scene, counts faces on splines too, counts vertices and lets you select any of these groups of objects. The dialog opens in a tiny window so it can stay open without using up valuable viewport space. It can be temporarily disabled and then re-enabled without closing the script.
This script is not bulletproof but I've used it in production on almost all scenes though I do recall an error once without knowing the reason. Use at your own risk. I will not be updating this one. Contact email@example.com with questions or feedback.
Run the script. If you leave it open it will update as things change in the scene. Use the small buttons next to each group listing to select all objects of that type. You can also temporarily disable the script. The script updates on a callback function to viewport redraws (like all the other counters). Sometimes when working in very large scenes the callback function can slow things down a little. Just use the "Disable" option and then press "Enable" when you want an update.