Biggest "bang for the buck" audio gear you have owned(in your history)?

DSPeaker Anti-Mode 2.0 Dual Core room correction unit with additional digital equalization if/as required. For about $850 it was/is a game changer, removing all bass issues from the room and taming a few 'hot-spots' on the frequency spectrum.

I believe once one hears a properly (flat) equalized speaker in a room one will not want to 'bypass' the unit to hear the garbage it removed. Night and Day.  Some eschew this correction; I say enjoy your lumpy bass. My unit will never go back.

Odyssey Audio Kismet stereo amplifier recently replaced a good-sounding W4S STI-1000 integrated. I dropped from 570w to 160w (8 ohm) and the sound of my system was bettered so audibly as to be laughable. Increased pure tonal density, air/bloom, still more clarity, deeper bass, and greater micro-dynamics. I have never been happier with a used audio purchase, ever. Pure dumb luck (research).

I'm going to say my least expensive component,  my Sutherland KC Vibe phono stage makes me think what a great value it is every time I play a record.   It kicks a$$ for the money.    Dead quiet and sounds fantastic.    Textbook example of trickle down that doesn't sound entry level at all.

I haven’t had much luck with finding great deals on speakers or DACs yet. I’m wondering how you guys are able find good discounts and prices? Are there good prices found here on Audiogon?

The best deals I’ve gotten have been on little novelty items like this Heathkit morse code oscillator that I got on eBay for practically nothing. It’s definitely just a trinket, but I’ve been able to do some interesting things with it.