simplest media to run NetBSD

[Darrel <levitch%iglou.com@localhost>]

Hello,

I have a specific goal and am seeking opinions.  The goal is to
make small, readily-reproducible read-only routing devices.  The
device will serve either as a gateway or bridge with main functions
such as filtering traffic, vpn, potential to graph traffic and the
like.

The software will vary, but it will be always be a BSD variant and
filtering will be with NPF, IPFW, or PF.  The question is about
hardware:

1)  should be read-only and load the operating system; therefore,
surviving reboots to the same state until the media is replaced
2)  should be inexpensive
3)  hopefully small but more than two Ethernet ports if necessary

cd-rom is familiar yet some folks are using usb sticks and perhaps
even other media that I have not considered yet.

This is the only list that I am subscribed to at the moment.  Thanks
to anyone that replies.

Darrel