General:
* Raw materials
* Commodities
* Earth's bounty
* Environmental assets
* Nature's gifts
Specific types:
* Minerals (for metals, gemstones, etc.)
* Fossil fuels (coal, oil, natural gas)
* Water
* Timber
* Land (for agriculture, development)
* Wildlife
More abstract:
* Environmental resources
* Renewable resources (solar, wind, hydro)
* Non-renewable resources
The best synonym depends on the specific situation and what you want to emphasize.