Clay might be a good item to trade as well. It's easy to come by, but a pain to get in any large quantity, plus river bees make it.
You'll be swimming in clay if you use Factorization ore processing. I was able to give away 1024 stacks the other day yet I still have 60k blocks to do something with.
If the server has equivalent exchange then minium shards/stones might be a good thing to sell.