Apple II
After a few somewhat esoteric systems (such as the Apple I, which lacked a keyboard, monitor, or case), Apple really hit its stride with the Apple IIe. The "e" stood for enhanced, as this was an improved version of the original Apple II, adding such useful features as the capability to display lower-case letters.
Anyone going through grade school in the United States in the early 1980s likely had a room full of Apple IIe computers tucked away somewhere in the school building, and for an entire generation of tech fans, it was their first introduction to a computer.
Macintosh
An ancestor to the iMac, the original 1984 version of the Macintosh was, like many computers of its day, a combination of desktop chassis and monitor, built into a single package. What set the Macintosh apart was its groundbreaking graphical user interface (some of us are old enough to remember having to use a command-line interface) and mouse--both of which were untested ideas at the time.
Of course, it's impossible to say for sure just how much the famous Ridley Scott's "1984" television commercial helped the first Mac. It's one of the most-cited advertisements of all time, but it only ran once on national TV.
iPod
It's hard to overstate the impact of the iPod following the fallow years in which portable CD players failed to become a cultural force like Sony's Walkman was. Besides the unique look and high capacity, the idea of a portable jukebox that could nearly instantly jump to any point in its catalog with a flick of a scroll wheel was revolutionary. Unlike (the very few) other digital music players, it was very portable, lightweight, and reasonably rugged, with a high capacity.
When eventually paired with the iTunes Store and 99-cent downloads, it was an unstoppable force. Apple still sells plenty of iPods, especially the current favorite iPod Touch, but the device's legacy may be in how there's now an "iPod" app built into every iPhone and iPad.
iTunes and iTunes Store
Many say, perhaps rightly, that iTunes is badly in need of a total rewrite, as it has become bloated and buggy, but it was a standard bearer in its heyday, and still the default for many people.
OS X
By controlling both the OS and hardware, Apple is in an enviable position of being able to make sure everything works seamlessly together, and more importantly, it makes it just a bit harder than Windows for a novice user to accidentally brick the system.
iMac
iPhone
Today, the idea of icons, apps, touch screens, and even traditional Web browsers on a phone are commonplace, but even the phones that have leapfrogged the iPhone in terms of components and features must surely admit their debt to the original.
Apple App Store
The search and discovery functions of the App Store have lagged behind the innovations of the devices that use it, but it's still miles ahead of the various Android versions, and the recent translation to OSX in the Mac App Store hints at a future where there's no rift at all between mobile and desktop operating systems.
MacBook/MacBook Pro
The early black and white polycarbonate MacBooks had a unique slablike look, as if they were carved from a single piece of material (although true unibody construction did not come to the MacBook for a couple of years). While we now think of MacBooks as high-end, expensive systems, half a decade ago the laptop market looked much different, and $999 was considered, if not inexpensive, then still a lot more budget-friendly than many other laptops.
It's hard to count how many laptops have been inspired by the look and feel of the MacBook line, from its island-style keyboard (which existed before, but was not nearly as popular) to its large touch pad, to the idea of finger-swiping multitouch gestures.
MacBook Air
Following the Steve Jobs mantra of design by subtraction, the 13-inch (and later 11-inch) Air lost the optical drive, most of its ports and connections, and every bit of bulk that was not required to make it functional. The Air played off of a largely unspoken truth about laptops--most people just use them to surf the Web and send e-mail--few of them get around to burning DVDs or using the eSATA port.
From the Dell Adamo to the Samsung Series 9, it's safe to say no pretender has truly managed to capture the mix of performance, battery life, design, and operating system features that make the current generation of MacBook Air laptops a top recommendation.
iPad
Lacking the two most common interface tools, a keyboard and a mouse, it instead relied entirely on touch, expanding on ideas laid successfully out in the iPhone and other smart phones. The final product had an element of sci-fi to it, evoking the retro-futurism of the slates and tablets we had seen in mockups and movie props for years.
In typical Apple fashion, the chattering classes were unimpressed at first. The iPad was too limited to be a productivity device, it lacked a camera, it was nothing but an oversize iPod Touch. From those initial mixed reviews, it has literally inspired an entire new class of consumer products, and the iPad's influence will be felt for a long time to come.