Killer app is familiar jargon to anyone who has spent any time around computers. The term refers to an application so sweet or so useful that just about everybody wants or must have it.

We’re showing you ours and we encourage you to show us yours. If you discover your own killer iPhone apps, by all means, let us know in comments so we can check them out.

1. Wolfgang’s Concert Vault

Wolfgang’s Concert Vault is an app that provides you with free access to the largest collection of concert recordings in the world. Some of our favorites include The Who, Led Zeppelin, King Crimson, Neil Young, Pink Floyd, Creedence Clearwater Revival, Elvis Costello, and David Bowie. And if those particular artists don’t appeal to you, you’ll find concert recordings by hundreds upon hundreds of other artists.

2. Instapaper

Do you ever come across a Web page you’d like to read later, when you have the time? Sure, you can bookmark those pages, but wouldn’t it be nice if you could somehow save them to your iPhone and read them at your convenience? And wouldn’t it be even nicer if you could read them without Internet access, such as when you’re on an airplane?

We’re happy to inform you that you can if you just download the Instapaper iPhone application from Marco Arment. Then, when you’re surfing the Web on your Mac, PC, or iPhone and see a page you want to read later, select the special Instapaper Read Later bookmarklet. From then on, you can read the page whenever you choose with the Instapaper iPhone app.

3. reQall

reQall is much more than just an iPhone app. It’s a complete and feature packed system that captures information that’s important to you and makes it easy for you to remember that info at the appropriate time.
The cool part is the unique way reQall works. You speak to the reQall application. Then and after a short time, your words are converted into text and sent to you by e-mail, text message, or instant message (or any combination of those three) as well as saved right in the reQall iPhone app.

4. Now Playing

We like movies, so we both use the Now Playing app a lot. Feed it your zip code, and then browse local theatres by movie, showtime, rating, or by distance from your current location. Another nice feature is the ability to buy tickets to most movies from your iPhone with just a few additional taps.

5. Pandora Radio

We’ve long been fans of Pandora on the computer. So we’re practically delirious that this custom Internet radio service is available gratis on the iPhone. It works on the iPhone in much the same way it does on a PC or a Mac. You type the name of a favorite musician or song title and Pandora creates an instant personalized radio station with selections that exemplify the style you chose.
Tapping QuickMix plays musical selections across all your stations. Tapping New Station, at the bottom of the screen, brings up the iPhone keyboard so that you can add a new station built around an artist, song title, or composer. You can also select from stations Pandora has packaged together around a particular genre.

6. Amazon Kindle

The folks over at Amazon made a splash with the company’s Kindle electronic readers. (When it comes to introducing high-profile products, we think the folks at Apple know a little something about making a splash too.) But although Ed is a fan of the Kindle reader, even he thinks they’re expensive — $359 on up at the time this book was in production.

Kindle for the iPhone, on the other hand, is perfectly free, though of course you’re still on the hook for buying electronic versions of books. You can do that from a PC or a Mac and wirelessly transfer them to the Kindle app. Or within the app, you can tap Get Books, which transports you to Safari on the iPhone. And from there you can purchase titles in the online Kindle Store. E-books for Kindle are deeply discounted compared to their physical counterparts; most new release bestsellers cost just $9.99.

7. Remote

Leave it to Apple to come up with one of the coolest iPhone apps money can’t buy (because it’s free). It’s called  Remote, and it lets you control music playing in iTunes on your computer, Apple TV, or AirPort Express.
With Remote, you can use your iPhone to do almost everything you can do in iTunes: Play, pause, skip, shuffle, search, or browse your iTunes library.

Better yet, you can perform these actions from anywhere in your house that has Wi-Fi. Remote is free, but it does require a couple of basics: a computer running  Apple’s iTunes software and a Wi-Fi network.

8. WhitePages Mobile

Yea, yea, we know: Plenty of phone directories are on the Internet. But WhitePages Mobile is an incredibly handy resource for finding home and business numbers on the fly or doing a reverse phone lookup (you have the number but have no clue whose number it is).

9. Shazam

Ever heard a song on the radio or television, in a store, or at a club, and wondered what it was called or who was singing it? With the Shazam app, you may never wonder again. Just launch Shazam and point your iPhone’s microphone at the source of the music. In a few seconds, the song title and artist’s name magically appear on your iPhone screen.

10. Skype

You’re probably thinking, “Why in goodness’ sake do you need an app that makes phone calls when you’re already carrying a cell phone?” Well, Skype calls are routed over the Internet through what geeks refer to as VOIP (Voice-over Internet Protocol). And if you frequently call friends, colleagues, or relatives who are overseas, you can save money by not paying AT&T’s lofty international rates. As with Skype on a PC or a Mac, direct calls made to other Skype members are free, and you can also instant message them. Through Skype, you can also call landline or mobile phones in the United States and around the world at low rates while not exhausting your monthly AT&T allowance.

The biggest drawback to be aware of: You must have access to Wi-Fi to make kype calls. Forbidding Skype calls over the 3G network is a restriction that we assume keeps AT&T somewhat satisfied.

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