In-flight Google Maps (second edition)
Six years ago, I was delighted by my discovery that I could pre-load Google satellite maps before a flight
to let me pan through the route as I flew over it, comparing my view out the window with the map. Until then, I'd looked at maps after landing, and tried to remember the features I'd seen and wanted to identify.
Some things have changed since 2005. Now, with in-flight wi-fi and an iPad, not only do I not need to pre-load (and worry about missing some zoom levels or portions of the flight path I'll want to look at), but I can follow along on satellite view with GPS!