Pc wise, definitely my SSD, Corsair Force 3 series.
Windows has never been the same, I'm the type who liked doing a gazillion things at once and have about 20+ apps that boot along with windows and having no more ''lockups'' due to the hdd being overloaded is great. Windows still boots very quickly despite loading a lot of crap on startup and is immediately usable and nippy from the moment the desktop is visible, unlike on the hdd where I had to wait for the app or browser to start for ages because windows is still loading.
I can't see how one would not be amazed with an SSD unless having an extremely clean pc, reinstalling every couple of months, not doing many things at once, etc... It's absolutely amazing if you have an older windows install (clone hdd to ssd for proper comparison). I tried multiple configurations and q6700+6gb+SSD is definitely faster to use than i7-12gb-7200 rpm conventional hdd. Yes for games the i7 pc is quicker but for normal home use and startup time, ssd speed over more ram and cpu power anytime.
GPU wise: Going from Fx5500 (was actually a downgrade from my previous Ti4200 I guess) to 6600GT.
CPU wise: Upgrading my p4 2.4 ghz into a 3.0ghz and clocking it to 3.9 ghz

.
Really amazed? The moment I upgraded my el cheapo Trust 5.1 set I bought for 35 euros to logitech Z5500's.
The moment I bought nice in-ear headphones ( well ''nice'' is relative, I bought a Goldring set for 40 euro's or so as opposed to cheap crap.).
I guess my car is also ''tech'', the moment I test drove my first V6, it sounded just so much nicer than that 4 cylinder crap I was used to hearing and amazed at the acceleration ( felt much nicer despite not being THAT much faster).
As much as I like gadgets and stuff, I wasn't that hugely amazed when going from k700i to a k750i to a Nokia N97, and then to a Samsung Galaxy s2 after that, I expected more. I was more amazed of my first mobile phone. (which was the K700i.)
Even recently going from 7-9 mb ADSL to 120 mb internet was a bit ''meh'', I actually downgraded to 40 mb in March to save me 2 tenners per month as while 120 mb is nice, 40 is enough and not worth 18 euro's extra per month imo.
I was amazed when going from 128k ISDN to 512k ADSL though back in 2000 or 2001 iirc, and all the following free speed upgrades every couple of years (until I reached the max I could get over ADSL on my address).
Loved my Gameboy color when I got it, absolutely hooked on that thing, ironically Pokemon too

, played it for 12 hours straight iirc.
Tbh, tech these days doesn't wow me any more as it used to, you need to spend more and more for smaller improvements...
In the old days I used to spend a couple of tenners or 100 at most on something and absolutely amazed with it.
These days I throw hundreds at my hobbies: Audio, PC, gadgets, etc... And it's all a bit ''meh'', is that it ?