[Photo from Connors934 on Flickr]
There are these great bikes at Maker Faire from XtraCycle. There is an extension that is bolted on in the place of the rear wheel. The chain is also extended so that it can reach the rear sprocket. Instead of a rack, there is a huge back deck, and along the sides are some nice panniers. Behind the seat is a set of handlebars for a second rider. The design is similar to the WorldBike.