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 for iPad app, you may never wonder again. Just launch Shazam for iPad and point your iPad’s microphone at the source of the music. In a few seconds, the song title and artist’s name magically appear on your iPad screen.

Being me, I decide to do my best to stump Shazam. I played wacky selections like Day Tripper by Sergio Mendes & Brazil’66, Joe Turner’s Shake, Rattle, and Roll, Book of Saturday from King Crimson’s Larks’ Tongues in Aspic, and even Dinah Washington’s What a Difference a Day makes. In more than an hour of testing every obscure song I could find in my iTunes Library, Shazam failed but thrice: Rockin’ Robin by the Jackson 5, Hot Venom by Rebirth Braass Band, and Justine by the Cretones.

When Shazam is right, which it almost always is, that song has been tagged (in Shazam-speak). Now, if tagging were all Shazam did, that would surely be enough. But wait, there’s more. After Shazam tags a song, you can:

• Buy the song at the iTunes store
• Watch related videos on YouTube
• Tweet the song on Twitter
• Read a biography, a discography, or lyrics
• E-mail a tag to a friend

Okay, I have to admit the Shazam isn’t great at identifying classical music, jazz, or opera, but that bothers me not a whit. It’s not exactly fantastic with obscure indie bands, though it has gotten better over time. If you use it primarily to identify popular rock music, it rocks.

The iPad version Shazam is free, with unlimited free tagging, as I write this. But the app’s description makes it clear that this is only a “lunch offer.” So I expect they’ve done with the iPhone versions of Shazam – a free version with five free tags a month and a premium ($4.99) version called Shazam Encore, which offers unlimited tagging and several other exclusive features.

I’ve tried other apps that claim to do what Shazam does. The best of the bunch for the iPad is SoundHound. It’s almost as good as Shazam – and it’s a hybrid app, too. That means it works with both iPhone and iPad for same price ($4.99).

And the iPhone app MusicID with Lyrics is at least s good as Shazam – and Probably better – for a lower price ($2.99). And though it’s an iPhone app, it works fine the iPad in 1x or 2x mode.

But Shazam for iPad is king of the heap – at least for s long as it’s free with unlimited tagging. If Shazam for iPad ups the price for unlimited tagging, SoundHound or MusicID with Lyrics are both excellent alternatives.

Shazam, SoundHound, and MusicID with Lyrics are all amazing. They work almost everywhere, too – in noisy airport terminals, crowded shopping malls, and even once at a wedding ceremony. Heck, Shazam is so good I gladly coughed up $4.99 for the premium version (Shazam Encore) for my iPhone.