For what it's worth I use the rings 319 posted quite frequently. My cargo trailer has three rows of 2x4 screwed to the floor I bolt the ring to. Temporary solution to a permanent problem, but as I don't ruin the floor I can unbolt and move them at will and destroy a $2.99 2x4.
L track for the floor is a great idea as are E track for the walls.
For what it's worth the have angled l-track you can bolt to your floor.
In my experience there is no one tie down that suits all. I myself will be outfitting my next cargo trailer with both E track and L track. In fact they make tiedown straps with both ends so you don't have to search for the appropriate fitting. Or better yet all the straps work anywhere in the van so you don't have to worry about how many of each you buy.
For what it's worth I've looked into the Snap-Loc system for my pick-up,
http://snaploc.com/.