On May 14, 1968, Paul McCartney and John Lennon went on The Tonight Show to announce the formation of their new company. "We've got this thing called Apple," said Lennon, "which is going to be records, films, and electronics."

The same quotation could have been made by Steve Jobs decades ago of his own company of the same name, if he foresaw even then moving beyond personal computing and into the realm of media distribution, epitomized by iTunes.

As you know by now, the two Apples have finally joined forces. After years of waiting, The Beatles come to iTunes today. Available for download are a box set that collects 256 songs, video of their first US concert, and a mini-documentary for $149 dollars. Individual tracks are available for $1.29, and individual albums for between $12.99 and $19.99 (for double albums).

The Beatles may be late adopters in the iTunes revolution, but throughout their careers, they were early adopters of unusual instruments, new techniques, and technologies as Lennon's intriguing mention of "electronics" on The Tonight Show suggested. Despite their delayed foray into the digital age, The Beatles were the most innovative rock band of all time, as this slideshow illustrates, and long after the group's demise, they inspired others to sample and experiment with the Fab Four's work, with or without their permission.

Some of the The Beatles' simplest, but most enduring, innovations were simply the introduction of a new musical instrument. Producer George Martin had the idea to introduce strings into McCartney's "Yesterday," an unusual move at the time. And in the summer of '65, George Harrison began to experiment with the sitar.

For "I Am the Walrus," John had the idea to run a live BBC broadcast of King Lear into the studio; the recording can be dimly heard in the finished track, says Beatles scholar Bruce Spizer.

The Beatles wanted a greater bass presence in their records. "Paperback Writer" is a landmark in the history of recording bass guitar, by transforming a loudspeaker into a microphone. Says Guitar Edge, "Engineers positioned the loudspeaker directly in front of his bass speaker cabinet, and the moving diaphragm produced an electrical current."

As in any laboratory, studio discoveries sometimes came accidentally. While recording the song "Long Long Long," says Spizer, Paul hit an organ note that caused a bottle of cheap Blue Nun wine to rattle. The group, digging the effect, set up microphones to capture the sound.

With a few of their singles, The Beatles became the first rock bands to try effects we now think of as standard or passé. At the end of the single "Rain," Lennon used a backward tape loop. The single "I Feel Fine," released in 1964, became the first commercial single to feature guitar feedback.

The Beatles pushed their sound engineers to new limits. Paul McCartney: "We would say 'Try it. Just try it for us. If it sounds crappy, OK, we'll lose it. But it just might sound good.' We were always pushing ahead: louder, further, longer, more different."

Near the end of his career with The Beatles, John tried his hand at avant-garde techniques in his work with Yoko. "Unfinished Music No. 2: Life With the Lions" contains a five-minute track called "Baby's Heartbeat," the sound of Yoko's unborn child. But she miscarried, and the following track is called "Two Minutes Silence."

In a recent concert given at Abbey Road Studios, Paul explained how the group circumvented the limitations of the four-track recording of the day: "What we used to do is take those three tracks and then bounce those down, combine those, to the fourth track so then you'd have all of that just on one track. And you'd wipe the other three, suddenly giving yourself more than four tracks, which is how you could do things like Sgt. Pepper, bouncing down all the time. Actually it gave the guitars an amazing quality. People would say, 'You're losing quality.' We liked this loss in quality. It made everything go all so shiny and ZZZEWWW."

For the vocals on "Tomorrow Never Knows," John ran his voice through a Leslie speaker, which takes advantage of the Doppler effect to create sounds typically on Gospel organ music. "It was those types of innovations," says Spizer. "They literally broke the rules."

Last year, The Beatles found an unlikely digital incarnation: as 3-D avatars in the popular game The Beatles: Rock Band. Paul McCartney and Ringo Starr poked fun at their uncanny new representations in a launch event.