Bonus: FanGuide LA Modern Architecture
Okay, this one is a little more specific, but if you have visitors in town, or just feel like learning something new about this city, it's still pretty amazing. Basically, the FanGuide app gives you 6 guided tours, each in different L.A. neighborhoods, focusing on historic and groundbreaking buildings throughout. Anyone who took an intro course or picked up a book on Frank Lloyd Wright could tell you there's some serious architecture in L.A., but this guide goes beyond the basics with audio guidance, tons of photos, maps, and a wealth of information. Because there's only 6 tours on the app, we couldn't really call it "indispensable", but the ease of use and the amount of fun you'll have on those tours makes it worth a definite bonus mention.
$4.99, available for iPhone only