There are lots of wonderful trailers out there. Carrying medium loads (100lbs or so) is pretty comfortable for most people. In fact many parents do this when carrying children. Any child trailer can also be used for cargo (er bikego) such as
this one. For larger loads above 200lbs, you want to be more careful because stopping distance is longer, you can't 'panic stop' if a car doesn't look, and steep hills are very much to be avoided. For these loads trailer mentioned above is fantastic. I
built my own out of aluminum as well.
You can view my
blog post or
my website for more information.