1) Hydrogen, whether in water form or not.

We do know that there is hydrogen at the lunar poles. This can serve a minimum of two ends: water for a base, fuel for rockets.

2) Oxygen

The heavy part of the liquid hydrogen/liquid oxygen fuel mix is the oxygen, which is about 7/8ths of the fuel mass. Instead of launching all the fuel for cislunar maneuvering from Earth, we could launch eight times the hydrogen from Earth and mix it with the lunar oxygen, which also is useful for breathing, making water and assorted chemical processes.

3) One-sixth gravity

This will provide engineering fun and challenges for future generations of engineers. How does one design an extensible tower for a solar mirror with one-sixth the force of gravity?

4) No weather

This goes hand-in-hand with No. 3. Engineering design will be significantly different in a vacuum environment with no water, wind, rain, hurricanes or tornadoes. Corrosion takes a different form.

5) Vacuum

The expenditure of large amounts of energy is needed to create a temporary vacuum here on Earth. The Moon has about 39 million square kilometers to operate in a vacuum.

6) Glass

A good proportion of the lunar soil returned by astronauts was in the form of glass. Lunar glass has the distinct characteristic of having formed in a water-free environment, making it anhydrous. What advantages this may offer in the field of optics is largely luna incognito. Then there's fiberglass, composites, etc.

7) Human factors

Since the Moon has only one-sixth of Earth's gravity, the heart does not have to pump as hard on the Moon to supply oxygen to the brain. While for a youth this would have an atrophy-type effect, for those advanced in years it can result in a rejuvenating effect, as the heart is suddenly relatively stronger. This allows for longer productive lives for our citizens.

8) Crater history

The Moon is the best record in our local neighborhood of the history of bombardments from space. Earth is too dynamic to sustain a record, but the Moon is perfect. By establishing an impact history in size and time, we can look for any cyclicality in the timing of impacts, and if so, determine where we are in the cycle.

9) Cold-traps

At the lunar poles, there are places the Sun never shines. These ever-dark craters seem to hold the bulk of the hydrogen detected at the poles. Excavations outside the craters can create additional cold-traps for later industrial use.

10) Solar mirrors

Mounted on extensible towers, mirrors can be placed in perpetual sunlight to illuminate selected areas at the poles. This requires the high-technology capability to turn a mirror. No batteries required.

11) Solar power towers

Extensible towers at the poles will allow the placement of solar cells or films in constant sunlight. It doesn't matter so much hitting the perfect peak for one's ground-based system as making the tower high enough to peek over the horizon, which on the Moon is very short. These might also be mounted with lightpipes to direct sunlight into sub-surface facilities.

12) Radio silence

While not a perfectly radio-silent environment, the far side of the Moon is far better than anything on Earth or even in orbit. Large arrays can allow for a leap in precision for radio astronomy and the search for extraterrestrial intelligence.

13) Solar cathedral

A number of religions and cultures around the world still use the lunar calendar in the conduct of their affairs. Part of this involves determining the beginning of each lunar month. Building a solar cathedral on the Moon will allow an unprecedented degree of precision in making that determination. It's also a good way of getting different faiths to work together.

14) Neighborhood watch

The orbital scopes like Hubble get all of the credit for cool deep-space discoveries, but no one's keeping an eye on our local neighborhood. That's why we're finding more and more asteroids after they've passed the Earth. The Moon provides the kind of dull, stable platform for the astronomy that no one else wants to do.

15) Greenhouses

Lunar regolith (surface material) can't really grow plants by itself, but the addition of humus, other nutrients and careful recycling does allow for plant growth. Plants grown in lunar soil may provide new fragrances, flavors and vintages. Spices were one of the early high-value, low mass/volume goods that helped create the trade routes of old.

16) Metals Vacuum-processed ultra-pure aluminum.

Vacuum-processed ultra-pure titanium. Vacuum-processed ultra-pure iron. Vacuum-processed ultra-pure magnesium. You want it? The Moon can have it.

17) Volatiles

The Sun has been burying light elements in the lunar surface for aeons. All it takes is a little baking at about 1,100 degrees Kelvin, a little shaking to agitate the particles and a place to liquefy the output. Cold-traps are particularly useful for this.

18) Extreme sports

Imagine bicycle races at 250 kilometers per hour, regoboarding the south side of Copernicus, flying in a large underground cavern and high-jumping or long-jumping in one-sixth gravity.

19) Spaceships

Some items, like advanced electronics, will be shipped from Earth for a very long time. But things like spacecraft structural elements (and fuel) can easily be done on the Moon, obviating the need to use precious lift mass from Earth's gravity well on things that can be manufactured on the lunar surface instead.

20) EML-1

Having such a large neighbor so close by creates a warp in Earth's gravity well. There are certain areas of relative stability known as Lagrangian points, where the gravitational pull between two or more bodies is equal. One of these, Earth-Moon Lagrangian 1 (EML-1), lies on the line connecting the center of the Earth and Moon. Putting a station at that point, (or rather in a halo orbit around it) allows for all kinds of unexpected benefits.

21) GEO assets

We have billions of dollars of orbital assets in geosynchronous orbit. It's cheaper in fuel to go from EML-1 to geostationary orbit (GEO) and back, than to go just from low Earth orbit to GEO. Over time, this will allow for a huge decrease in the cost of refueling, repairing and upgrading, as well as building larger and more capable platforms.

22) Solar power satellites

Placement of large solar arrays in geostationary orbit allows for the collection and transmission of energy to fixed points on Earth, such as military bases. This will also provide a long-term source of energy, as the Sun is not expected to expire for another 4.5 billion years or so. Besides, most of the energy we use here on Earth is second- or third-hand solar power anyway. Pieces of the solar power satellites, like photovoltaic cells and structural elements, can come from the Moon.

23) Free-flyer platforms

Another consequence of the warping of Earth's gravity well is that trajectories can be created that sort of wander out from EML-1, and then wander back (like the Genesis mission which went via EML-1 to the Sun-Earth Lagrangian Point 1 and back). This affords materials scientists and companies the opportunity to send free-flyer platforms on long-term, jitter-free production runs. Results can be studied on the station and new production runs undertaken quickly.

24) Constant access

The entire lunar surface is accessible 24 hours a day from EML-1 for about the same delta-V ~2.5km/s (approximately 2.5 kilometers per second). From EML-1 most inclinations of low Earth orbit are accessible for less than 1.0 kilometer per second (with aerobraking and time, ~3.77km/s for a direct burn). GEO is constantly accessible, as is deep space.

25) A true spacefaring civilization

The Moon is the ideal location to get our feet wet, and getting there can lay the foundation for a civilization that can go beyond the Moon to Mars and the asteroids and other destinations of interest.