The OLPC XO Serial Adapter Kit $25
works on my DreamPlug at half the price.
The only proviso is that you must connect Black, Red, Green to Ground, Rx, Tx (respectively) rather than the way you would if you were connecting to an XO.
No soldering involved. It comes with the correct connector.
It's very small and much more convenient than the expensive one provided by Globalscale.
You could also consider Adafruit's FTDI Friend: http://www.adafruit.com/products/284
but you'd have to also get the correct connector- one of the "picoblade" products from AMP.
But you'd have to figure out how to connect the wires- I haven't figured it out yet although haven't tried very hard because the XO adapter works very well.