One of our users (Olzeke) found this prototyping board meant for Parallax's BASIC Stamp. It breaks out the 24 Stamp pins to through hole pins. Makes soldering easy. The ARMstamp inner 24 pins are compatible with this board. You can buy these prototyping blank PCBs from a Canadian supplier PCBoard.ca for $1.95 each.
Just use some 1x12 single row male and female headers and plug the ARMstamp in. No need to add either the RJ11 or power supply components. The USB connection of the ARMstamp will supply 5V to the board up to the limits of the PC (typically 500 mA) or your USB wall wort (I've seen more than 3A available)
Here are the inner 24 pins of the ARMstamp that match those of the BASIC Stamp. With additional features like A/D converters.