Well not really trade, but rather purchase goods and mercs at local prices. I can't remember off the top of my head, but I believe treants and ogres are both big carrier units for the other races.
Must admit, as i seen humans have the best towns, even better than elves =).
Doug is working on the elven towns as I type this, and I can assure you that you're in for a treat.
Don't hold us to this as things may change during the design phase, but the plans for the elven towns include a gorgeous enchanted marble citadel, healing grotto caves, sea walls, and an inhospitable archipelago settlement deep in the elven swamp where the elders speak of an evil deity lurking outside their eroded walls.
Glad you all like these new towns! They should look a lot better too - I was having trouble getting the 3D grass to load. =/