Connectors and receptacles for easily plugging and unplugging cables
FCI, and Molex both make a line of plugable screw terminals if you want to go that route.

http://portal.fciconnect.com/portal/page/portal/fciconnect/producttype?appname=catDisplayByPath$entryPoint=adir%20%20ect$categoryPath=Product%20Type

http://www.molex.com/molex/products/family?key=eurostyle_terminal_blocks&amp;channel=products&amp;chanName=family&amp;pageTitle=Introduction&amp;parentKey=terminal_blocks_and_barrier_strips

http://www.molex.com/molex/products/family?key=mtc_multi_terminal_connector&amp;channel=products&amp;chanName=family&amp;pageTitle=Introduction&amp;parentKey=terminal_blocks_and_barrier_strips

A better idea might be to use ribbon cable with shrouded headers.  The shroud will give you the polarity protection you want. You don't need any special crimping tools to make the ribbon cables they just snap together.  Here are some links to examples of 6-pin cables in a 2x3 header.  These are really common and come in many sizes though.

https://www.sparkfun.com/products/10651

https://www.sparkfun.com/products/10650

https://www.sparkfun.com/products/10646