If you know anything about high-end audio gear, you know about Stereophile. Founded in 1962, it has become the bible of the high-end with in-depth reviews of equipment and music.
Each year Stereophile publishes its list of recommended components, and now that issue, Stereophile Recommended Components 2012, is free on the iPad as an app.
Of course much of the gear is expensive -- like speakers systems selling for many thousands of dollars -- but you can work your way down in price and sonic accuracy, and usually find quality items you can afford.
The iPad app is complete, with mini reviews on hundreds of components, from turntables (remember those?) to headphones to amps and pre-amps. Many of the capsules link to full reviews with an online link. Even the Apple iPod classic gets pretty good marks for audio quality and the ability to play many different audio formats.
If you're into high-end gear, or just want to lust after things you can't afford, I recommend the Stereophile iPad app. Of course I have a couple of quibbles. The app works in portrait mode only, which is really silly since many people are using their iPads in landscape mode. This app shouldn't force a choice. It's especially irritating if you are using a landscape iPad stand or case. Second, page turns require using a small arrow key at the bottom of the app. It would be a lot nicer if the app supported swiping turns so you can graze more naturally among all that great content.
Having said that, the Stereophile app is a great resource, and if you are into high-end audio it's a must have.
The app is a 6 MB download and requires iOS 5 or later.