There are lots of datasets available for reuse. A small sample is below, but there are many more.
Just be sure to read the requirements for using the data, and don't forget to cite it.
- Global Biodiversity Information Facility: Biodiversity data
- CoRIS: Coral Reef Information System, a portal with data and information from NOAA
- Figshare: Data from researchers in many different disciplines
- Dataverse: Data from Harvard researchers. Filter by discipline, date, and more.
- Data.gov: Government data including ecosystems, maritime data, and climate data
- USGS: Data from USGS scientists, including energy, water, and ecosystems data