Connections, Pins, Plugs, Adapters, Breakouts, Etc.
It may sounds strange to say, but this is a vast and a vastly complex subject. The 'this' referred to does not even have a consistent, coherent name ( IMHO ). Connections and all that kind of stuff ...
Picky little 'this' connector issues can be a more critical success factor than the actual underlying electronic technology. See ArduinoProMini and ArduinoTeensy for concrete instances.
https://en.wikipedia.org/wiki/Electrical_connector
https://en.wikipedia.org/wiki/Category:Electrical_connectors
https://en.wikipedia.org/wiki/Category:Computer_connectors
Test Probes & Leads - https://www.amazon.com/Test-Probes-Leads/b/ref=dp_bc_4?ie=UTF8&node=5011673011
http://forum.arduino.cc/index.php?topic=53385.0
Topic: Mini Pro (or so) - temporary connecting pins without soldering? ...
Pogo pins sound interesting, but blimey these are pricey. These http://www.farnell.com/datasheets/60455.pdf 'kinky pins' at Farnell look interesting as well.
http://www.oxleygroup.com/product/kinky-pin-terminal-connector
http://www.oxleygroup.com/components/interconnect-products
http://www.newark.com/oxley/040-30p-kp2-l-silver/terminal-kinky-pin-pcb/dp/11N6269
10 for $12.80, or so. Plus a one-time shipping surcharge fee of $20 ???
How many dollars to a pound ?
http://forum.arduino.cc/index.php?topic=53385.0
... As a 'hack' for programming a Mini Pro I push 6-way pin header into the end and then apply pressure with my fingers to slant the connector and keep it in contact with the thru-holes. Fortunately the impedance of my fingers isn't too low to disrupt the programming process(!) ...
These pins are spring loaded and $0.70 http://www.farnell.com/datasheets/38286.pdf
https://learn.adafruit.com/how-to-make-a-pogo-pin-test-jig
USB
A strong preference for USB, except maybe ... FTDI ?
https://www.moddiy.com/categories/Connectors/USB-Connectors/
Big Issue: Need for very short custom cables, less than 4", impossible to find at any price, probably must make myself.
DIY USB Connectors - https://geekhack.org/index.php?topic=44924.0
12 Volt Connections ?
https://en.wikipedia.org/wiki/Cigarette_lighter_receptacle
Note how Trac paths make the anchor name "#a12VoltConnections"
Resources
https://en.wikipedia.org/wiki/DC_connector
http://www.newark.com/browse-for-products?ICID=MNAV-A-all-categories
... 1,463,844 Products Found ...