Jen sent a link to the new TerraCycle Cargo Monster kit, which I though warranted a mention. You can use it to convert your tadpole trike to an Xtracycle-enabled cargo hauler, and even convert a 20" rear wheel trike to a 26" wheel. 

Photo is from bikeportland.org's flickr page. 

This joins the RANS Hammertruck as another sweet cargo hauling option—you know, if a Big Dummy is too vanilla for you. If that's the case, you're probably as eccentric as a Bushnell Bottom Bracket, but that's A-OK with us, partner.