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. 

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

Audio Research SP10II. Bought in '85. Used thru 2010. My current Silverline Boleros. Quad 63s USA Monitors and an Threshold SA 3. All great stuff, then and still.
Placette passive Remote Volume Control--replaced a $15k Mark Levinson preamp back in 2001 and sounded better. $1295.

used it for 3 years and loved it in the context of a $250k system.
Dynaco Stereo 70.  Bought it used for $50.  Used it for nearly 30 years mostly stock, then added a VTA PCB, and new caps and tubes for another hundred bucks or so, and still use it in my main system today as half of a bi-amp situation.