Thanks to everyone for your replies.

From: Terran Melconian
There are literally hundreds to choose from, but here are a couple
example part numbers I pulled out of the Mouser catalog to point you in
the right direction:
Header: Mouser 517-2312-6111tg, 3m 2312-6111tg
Socket: Mouser 517-974-01-02, 3m 929974-01-02 (board mount)
the sockets also come for crimp pin or IDC connections.

That should be a big help - I just needed some keywords: header,
socket, board mount, IDC.

From: kony
Male pin headers and female socket connectors with 0.1" pin
spacing. Also socket contacts (inserts) are often sold
separate from the socket itself.

This helps...

What exactly are you looking for? Straight plastic sockets
with 0.1" pin spacing but do they have to be the very thin
(black in your links) type such that on a row of pins in a
pin header, you could plug in two right next to each other,
OR could the plastic connector body be larger like those
used on fans? The point is that if looking for an
especially low price, one option is surplus electronics
'sites which may have something that would work (or may not)
depending on the requirements beyond the basic # of pins,
spacing and pin size.

This would be a way to make certain components (such as pots &
trimmers, 1/4" phono jacks, switches, or other sub-circuits) "plug and
play" for various prototypes + experiments. The motherboard size
headers are small enough where the leads match the components I'm
using and the pins on a motherboard that LEDs plug into are just the
right size to plug into a solderless breadboard, but are more durable
than the regular breadboard jumper wires.

You might check the following surplus sites (and ebay).

Thanks again