Hard to beat ForeFlight for geo-referenced tracking on sectionals, IFR low/high, and with the Pro version, approach and taxi charts. Also includes many FAA pubs (free), flight planning weather graphics and flight plan filing.
I have it on two iPads and an iPhone for the single subscription price of $75/yr for the basic version or $150/yr for the Pro version.
See
www.blog.foreflight.com for more info. It won't disappoint.
