In Civ III, we've divided Wonders into two categories: Great Wonders and Small Wonders. Great Wonders are essentially what we used to call simply "Wonders". They can be built only once, and are winner take all -- whomever completes the Wonder first reaps the rewards. Small Wonders are a new type of Wonder that can be built by every civ, but only once.
Another interesting thing about Small Wonders is that they are not enabled simply by researching technologies. Most of the Small Wonders become available after certain gameplay conditions have been met by a player. For example, you cannot build Wall Street until you have at least 5 banks. Other Small Wonders can depend on a variety of things, such as SDI, which requires the Integrated Defense technology and 5 SAM missile batteries to construct. Also, Small Wonders in a city are destroyed when that city is captured, whereas Great Wonders can be captured. Finally, while Great Wonders can be made obsolete by new technologies, Small Wonders cannot.
We've also made some changes to the Great Wonders. Great Wonders can now be "rushed" to completion only under the direction of a Great Leader. Great Wonders are also now associated with one or more of the Civilization strengths (see the Developer Update). If the attributes of the Wonders you've completed match your Civ's strengths, you will trigger a Golden Age. For example, the Chinese are "Militaristic" and "Industrious". If they build The Art of War and Hoover Dam, this satisfies both strengths and a Golden Age would begin. A far better tact for the Chinese would be to build the Great Wall, which satisfies both strengths at once and would immediately trigger a Chinese Golden Age upon completion.