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. 

Well it's not my favorite piece of gear, not by a long shot - but purely based on "bang for the buck" I am hard-pressed to name anything that has squeezed out $400 of value as much as my old Bluesound Node2 that I picked up 5+ years or so ago.
Constellation Inspiration Preamp 1.0 and Stereo 1.0 - TAS 50 Greatest Bargains in High-End Audio

New Lyra Etna cartridge at half price.

Used Van Den Hul Grail SB - plays with the big boys