Inkjet Printer - We got an Epson Stylus Color with the Compaq Presario 486 SX2 66 and we printed out a relatively low res picture from Encarta. A sopwith pup. The previous printer we had was a dot matrix on a Commodore. It was amazing. I remember my dad said it he was, "thoroughly God damn impressed"
Cell Phone Text Messaging - Had a Nokia that was the first phone that I bought and first cell phone. When I found out that I could text people it was a game changer. Don't have to try and hear what was being said, I could read it. Just friggin' wow.
ICQ - Email was impressive, but instant messaging was very impressive. Still remember my UIN but unfortunately can't login to it (not that it'd work anymore anyway)
MP3s - When I found that I could download music I had to give it a shot. I downloaded a few MP3s over dialup and this was pre Napster days. Backed up the songs on floppy and had to play them in DOS on my computer. I remember one of the first was The Distance by Cake.
Writable CDs - Was one of the first kids in my school with a CD burner (bought it for $240ish) and installed it on our aging computer. Burned a whole bunch of coasters because of the dreaded buffer overrun. Felt there were unlimited possibilities when I could burn stuff to disc.
Divx - Video compression pre-Divx was not great. Divx was the first time it made it feasible (from my perspective) to download good quality video from the internet (we had some horrible dialup).
DVD - The jump from VHS to DVD is something that'll be hard for people to understand if they started with DVD. DVD is fine, Blue-ray is obviously better but not as drastically noticed as VHS to DVD was. My brother worked at Circuit City (RIP) and he got an Apex 300A. We managed to find the secret menu to turn off Macrovision and we were recording rented DVDs onto VHS. Sounds dumb, but it felt revolutionary.