I would sat DAT , Getloaded.com and Internet Truckstop are the big 3. Which is the best I could not say and to move intra US is illegal for us Canadian carriers although many do it.
@Rob ... actually it's not illegal for you to do it as a carrier. It is illegal for your Canadian born drivers to do it. If you have aboriginal drivers, U.S. citizen drivers, or foreign drivers that have a temporary work visa for the U.S., you can put them in your trucks and haul point-to-point in the U.S. If you decide to do it anyways, and do get caught, you'll get a $400.00 fine and your driver will be red-flagged for a while.
As for load boards, I use CHRW Trucks, TQL, Hub Group, Landstar, Lakeside, SPI, FedEx, GetLoaded, LoadSurfer, Freightview, Internet Truckstop, and RealTime. All of them together don't cost as much as my LoadLink subscription !!!
True I myself did a couple when I have a status card carrying native work for me a few years back. I also did a FEMA load during an emergency a few years back where I dropped a guy out of the Peg and loaded him with water in ND for somewhere in the south(cannot remember thinking Alabama) and the driver was given a letter stating FEMA load and cabotage rules where not to apply as well as a free pass on HOS rules until delivery.