Tree = Log (should be apparent, but jic)
Due to trees being a renewable resource, probably a good idea to monitor the buy/sell on those... they take awhile to grow, but you cam generate quite a bit.
Fish/Wheat (to a lesser extent, pork) would be cool to see on there, simply because it would give people an incentive to farm/fish/swinocide, and bread could be a lot more viable as its pain in the ass to benefit ratio is pwnd by the red army of pigs infesting the land.
Also, have you come to a ruling on the creeper spawn/sulfur as purchase item only? I AM ON THE EDGE OF MY SEAT!