The ones that made me go WOW, (and I mean "jump in technology" wow, not "I haven't upgraded my PC in so long its a jump" wow):
(1) Creative Soundblaster
The jump from PC speaker effects/music to sound cards was bigger imo than any jump in the CPU/GPU market, bigger even than the performance HDD to SSD transition, and the Soundblaster was the Geforce of audio.
(2) Nvidia Geforce
Bigger imo than any other GPU jump including Voodoo, mainly because it brought about the beginning of the end for 3DFX, and mainly because it was such a big leap that ATi/3DFX didn't even respond with their next gen, they had to respond with multi GPU versions of their current cards and try to catch up in time to battle the Geforce 2.
(3) 3DFX Voodoo
The first 3D accelerator, boom.
(4) Compact Disc
CD > 3.5" 1.44MB floppy, that is all.
(5) ADSL
56k modem to 256k ADSL was a 5x jump but the biggest difference between dial up and ADSL was the latency drop. For the first time UK clans could compete with Euro/US clans on a level field (and compete with each other lag free).