Which components knocked you out on first listen?

Without a single trace of doubt: Tidal Contriva loudspeakers (the 2005 model with ceramic mid drivers) last May.
I had been looking for "definitive" speakers for over 3 years and auditioned a number of B&W 8 series, Wilson Audio Sophia, Audiodata Avance, etc., and yes, I had also heard Avalons at audio fairs. In the end, I was "sure", it would have be the Sonus Faber Amati Hommage.
And then, I sort of stumbled across the Tidal Audio website. I had never heard of the equipment but was intrigued. It turned out, in Germany there aren't even stores that sell the equipment, so a pair of Contrivas was delivered to our apartment by the Tidal people for auditioning (250 kilos two stores high, poor blokes). They didn't have to worry about lugging them down again: After some Ron Carter, Rosa Passos, Sarah K., Marc Moulin and Glenn Gould both my wife and I knew we had to have these and sat listening to music until very late in the night! 3 years against a half hour to find the Holy Grail of Speakerdom! And, never mind their weight, they look blindingly beautiful on top (look at Audionut2005's system - hope you don't mind Jörg)

I first listened to Martin-Logans in 1994 and immediately bought a pair of Aerius-i speakers, since I couldn't afford anything beyond that price point. A number of different speakers followed during the next 12 years (eg, B&W, Tylers, Thiel), but in 2005 I finally found the speakers that I'd been pursuing ... C&C SuperAbbys and Bailey sub. After 15 months, it's still a total thrill to listen to music through these wonderful speakers

MIT power conditioning products while evaluating top level Krell and Mark Levinson power amps. Stunning !

KLH Model 9 electrostatic speakers with Marantz Model 9 and/or Futterman H-3 amp with a Dyanco PAT3 preamp. Turntable was either a Toshiba which had a pencil thin arm with an electret cartridge or it was a Garrard fitted with a Stanton EE. It's been a while (late 60's) but that's a general idea of the set up.

Quad 988.
Klipschorn and many other klipsch speakers were my main stay - but I had been wanting to improve the midrange tone. Heard many other "high end" speakers JM Focal, Tannoy, 801's, and on and on... sorry to all who disagree, but Klipsh's design from the 1940's beats them all. BUT... When I heard the 988 - I thought I had gone to heaven - brought a pair home then very next week. Happily ever after...