Hidden Trenton (which has extensive coverage of hiking) just published 3 geo-registered pdf maps of central NJ hiking areas (Baldpate, Sourlands, and Witherspoon Woods/Mt Lakes). They're free for download here:
The webpage also provides detailed a description of how you load them into your smartphone using a free app called Avenza PDF Maps. Essentially, it uses the georegistered PDF as a basemap, and provides full GPS-like capabilities on your phone (drop waypoints, record tracks, measure distances, etc). Significantly, it works even if your cell phone loses its signal. Plus, once you've downloaded the PDF map (which you can do on wifi), there's no data usage.
More maps are coming. I'll continue to post announcements as they emerge.