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

This is very subjective, and your opinion on your own systems/items is all that really counts.

From the beginning to now, these would fit that category for me: (in no order)

Original Large Advents
Dahlquist DQ-10
Conrad Johnson ART pre.
Original Monster interconnects and speaker wires.
Nakamichi SR-3a
AR Turntable
Audio Research LS-12
Magnepan 1.6
Magnepan 20
Wireworld Gold Eclipse III
Audio Technica Electret Condenser headphones 
Magnum Dynalab Etude and 108 tuners
Magnum Dynalab Receiver (original)
And in those "early days" special pressings and imported Jazz albums. 

There may be others I am forgetting, but these were very good items along my journey. 

Parasound Halo stuff


Pass Labs for sure
Some ARC
I built a pair of Bottlehead Paramour 2A3 set mono-blocks about 15 years ago. They were a fantastic bargain at the time. They sounded great with efficient speakers and they were fun to build. Mine turned out beautifully. I sold them years later here on A-goN.
Just picked up a new 3B+ for $35. Sounds better than my BluSound that got banished to the back shed. 
Rectilinear 3A speakers
Rectilinear 7 speakers
GAS Son Of Ampzilla (original) Power Amp
Large Advent speakers
Nakamichi Dragon Cassette
Teac A3400 Reel To Reel
Accuphase T100 Tuner
Thorens TD125AB MK II turntable and arm
Shure V15 Type 5
Ambient 66 Speakers
Audioquest Indigo Blue speaker cables
Odyssey Stratos Extreme Power Amp
Golden Ear Triton One speakers