Leaps and important moments I experienced first hand:
Doom & Quake: While today we take them for granted and we've heard countless of times the importance of iD's most important works, experiencing directly the roar they caused was something else. There a reason why, almost 20 years later, iD's still enjoys some credibility despite having an almost 20 year-span of barely good to quite mediocre releases.
Game graphics never the same.
1998 games: Specially Half-Life and Metal Gear Solid. These two did for gaming's narrative possibilities what Doom and Quake did for graphics.
Pentium III (Specially Tualatin): Would you believe there used to be a time where some folks at the tech industry believed that architectures like RISC and PPC would overtake x86 and Intel eventually? Well, these voices where silenced with the Pentium III. A speed demon that also was a tech miracle, spawning both desktop and mobile solutions, Pentium III is, arguably, the processor that saved Intel. The Pentium 4 almost derailed the company again, when they were more interesting in Ghz numbers and not in actual performance. This era is also known as 'the days AMD used to be actually a credible alternative'.
But since the iCore procs appeared Intel have never looked behind.
CD Writers: Some members here are too young, but the idea of having such massive space (700 MBs!) for backups was all the rage back then, and they were cheap! This was a time where many companies where trying to thrive in a space-needy market with proprietary solutions (Remember ZIP and JAZZ?).
3dfx: Do I need to explain?
WI-FI: Another tech we take for granted, but it was massive in the 90's.
And the two things I suspect many will try to cut my throat:
The iPod: Yes, there were already many MP3 players in the market, personally I used to have a Creative's Zen XTRA. But for those of you who can remember, MP3 players felt somehow of a fad and the industry actually did not trust the technology entirely –this produced a series of portable audio experiments like Sony's MD–. The iPod, arguably, is as important in the portable music history as the first Sony's Walkman. It popularized these kind of devices to a point where now we hardly hear the term 'mp3 player' as it's been replaced by 'ipod competitor' or simply 'ipod'.
The iPhone: I will synthesize my opinion with the following image –ignore the Samsung text, my comment is directed to the general world of pre-iPhone smartphones: