bicycle trailer hitch - Google Search
Radical Design Bike Trailer Hitch Radical Design http://www.amazon.com/dp/B00I8VTUOU/ref=cm_sw_r_pi_dp_cOu7ub0Y91EW7
seatpost hitch - Google Search
bicycle trailer hitches
KHS Tandem Sport
Haulin' Colin Bike Trailers
really cool tilting bike.
HH Max Cargo Bike Trailer. (Doubles as a hand cart)
I saw this design on a folding bike and thought it awesome. I used to hitch my bike trailers with a lashed inner tube, but this is faster and more convenient. Works very nicely.
IC 349 Integrated Manufacturing Project