Hi Steve - if you switch from "free rotation" to "Rotate around world z axis" under Options > View > Rotate/Pan/Zoom options > Rotation style, it should un-tilt the view at that time, so that's one way to do it (switch temporarily to free rotation and back out of it, since it's at the time that it is switched that it will relevel).

Another way is to go to Options > View > 3D view angles, and the 3rd input field on that dialog for "Tilt angle" can be set to 0.

If you need to do a bunch of them, it's possible to automate either method with a script - here's one that you can set on a keyboard shortcut that sets the tilt to 0:

script: /* untilt view */ moi.ui.mainWindow.viewpanel.getViewport('3D').tiltAngle = 0.0;

- Michael