Probably the resource that I would most like to see is copper, both for the Bronze Age and then you have to have it to research Electronics, Robotics, etc. No copper, then you would need Aluminum, which is not as good, or use gold.
As for resources that are being missed, some of the world maps that I have looked at completely lack any spices coming from the Central America area, where you get Vanilla, Chocolate, and Hot Peppers, to say nothing of Allspice.
Also, during Carthage's heyday, the Carthigians tamed the forest elephant subspecies that lived in North Africa at that timed, and used them against Rome. Hannibal started his march over the Alps with the 37 that has survived the march from Spain. By the time of Cannae, he had one left. The Romans exterminated the North Africa elephants for use in the Roman games. So, if you are making an Ancient World map, put elephants into North Africa.
For you guys looking for ideas on resources, that a look at some of the scenarios that come with Civ3Complete, as there are a bunch of good ideas in there. There is also one set of scenarios, the Test of Time series, where you have varying yields from the same resource, which really makes for an interesting game. You might ignor the spot that has only one fish for a food resource in a bunch of mountains and desert, and find out later that the fish was worth 25 food. He does the same thing with cattle, and has added sheep. The varying resource value is something that I am going to play around with.