Add a layer to QGIS from an ArcGIS REST service

1. Go to a REST service page and pick a layer
   • For example: Georgetown city limits (http://gis.gscplanning.com/arcgis/rest/services/CityLimits/MapServer/0/)
2. Copy the URI
3. In QGIS, click Add Vector Layer
4. In the dialog box, select the Protocol option.
5. Paste the service URI into the URI field
6. To the end of the the URI paste query?where=objectid+%3D+objectid&outfields=*&f=json
7. Click Open

This method works best for services with <1000 features.

Source: QGIS Wiki