I built this from an old tandem baby stroller and wheels from some bikes I pulled out of dumpsters.

The main outer frame is the handle from the stroller. The supports are just the supports from the same stroller.

The tow-bar is electrical conduit and attaches to the trailer with a part from a golf bag caddy.

The hitch, (I'll have to get a decent image of it), is the metal portion from a caster, similar to this one:

With the caster mounted sideways and the wheel removed, a hitch-pin fits nicely through the hole where the axle used to be. It gives the trailer a full range of motion.

I attached the hitch to the bike using two U-bolts around the chainstay.

I can also put a larger bin on to this baby. I've hauled over 100 lbs of groceries, cat litter and pet food.
It can also hold an airline kennel for hauling our black lab up to the park and whatnot.