In a previous post I featured Bikes At Work's trailers for converting your bike to a work bike. These will undoubtedly become a primary means of transport as the economy shifts to a post-petroleum future...(watch for more donkeys and horses, too.) Here's a few more sources for work bikes:
Worksman Bikes: I first learned about these folks through CoEvolution Quarterly (Whole Earth Review): "Worksman Cycles has long been known as the world-leader in Industrial Cycles (Bicycles and Tricycles). Today more than ever, leading companies call upon our Worksman Business Cycle System to safely and efficiently move key personnel and supplies within large industrial facilities. Our customer list is incredibly diverse and impressive, featuring the world's largest and most respected companies. These companies know that for durable, emission-free transportation, Worksman Business Cycles are the only smart choice." The vegetable delivery cart (which I'd love to have) and the hand-pedaled bike are very cool.
International Surrey Co., LTD: "Offering the finest four (4) wheel Surrey bikes in the world. No other Surrey bicycle company has rented, distributed and manufactured these distinctive four wheel bicycles. Our pledge is to continue to offer innovative two person and four person four wheel Surrey bikes for your business or home and CYCLES THAT MOVE YOU™."
Check out this Wiki page featuring work bikes from around the planet, many of them homemade.