So what was so special about the Apple II? It offered plenty of productivity tools (including being the first PC to run the VisiCalc spreadsheet), it was good at gaming, and it was quite extendable (when's the last time you had a computer with eight expansion slots?). And the machine itself looked so much cooler than anything that preceded it, a philosophy that still lives on in the Apple computers of today. The Apple II may not have been the first personal computer, but it was the spark that ignited the personal computing industry.

If you're lucky, you might still be able to find an Apple II on Ebay, though they don't seem to last long. 

3. TiVo HDR110 (1999)
It's hard to believe but it's true. TiVo has been around for almost a decade, making it nearly geriatric in the world of tech. The premise is simple: TiVo (and its competitor ReplayTV) replaced the VHS tape with a monster hard drive, recording shows to disk instead of analog media. That meant you could pause and resume live TV, skip through commercials in an instant, and record an entire season of shows with just a few clicks of the remote control. TiVo's innovations (it is now up to its Series3 model,) helped it to handily beat ReplayTV in the battle for mindshare, though it struggled to reach profitability and now risks falling prey to that killer of many a promising company: commodity status. Though TiVo the brand may eventually die, "tivo" the verb will probably be with us forever.

4. Napster (1999)
No, we're not talking about the current Napster subscription service, which pretty much has nothing to do with Shawn Fanning's groundbreaking file-swapping software. Say what you will about how Napster facilitated copyright violation on a massive scale (it had 60 million users, at its zenith), but piracy was around well before Napster came along and continues without it.

Rather, Napster is of critical importance not only for inventing peer-to-peer technology, but also for forcing record labels to play ball and work with tech companies to legalize the digital music industry. Even P2P is finally on the verge of legitimacy, as companies such as Warner Brothers and Paramount have recently signed deals to distribute content through P2P upstarts BitTorrent

and TV streamer Joost.

5. Lotus 1-2-3 for DOS (1983)
Whenever the topic of killer apps comes up, mention of Lotus 1-2-3 is never far behind. 1-2-3 was the PC's first critical application, and it was almost single-handedly responsible for giving the PC the major push it needed, past all other competing hardware platforms, to become the de facto standard for business users. Lotus 1-2-3 wasn't the first spreadsheet app, but it was visibly superior to competitor VisiCalc, and it remained the standard until the rise of the Windows era and Microsoft Excel. Lotus chose to throw in with OS/2 instead of Microsoft, alas, ultimately sealing its fate in the market, though it lives on now as Lotus 1-2-3 Millenium Edition. 

And if you could kick yourself for tossing out your old version, $20 or $30 can get you a copy of Lotus 1-2-3 on eBay.

(To see the other 45 best tech products of all time, visit PC World.)