There are a variety of Long John type cargo bikes; Bilenky makes one, for example. They're something like my Counerpoint Opus II tandem, with a smaller front wheel steered with a linkage, but instead of the stoker lounging around on a beach chair out front, you have a cargo box. Being able to see the front of the bike is an advantage; I can maneuver the tandem through remarkably tight spots, whereas the xtracycle is a little trickier on turns.