Question Web sites to offer hauling?

[ponyuk]

I have a trip out to DFW, TX from L.A. towards the end of June. I'm taking a fairly small approx 500 cubic feet trailer with enough belongings to keep me going until my moving truck arrives. I'll be driving back to Los Angeles around June 29th to collect the last of my belongings, and the pets.
I have 500 ft of empty space coming back, which I am sure someone is willing to fill and pay for. I posted an advert to craigslist but wondered if anyone knew of a site specifically aimed at connecting shippers with all these empty trailers on the interstates?