Here's a list of web-based sources of data. These are sources that are useful for certain kinds of projects, but you might need other kinds of data as well. One strategy to try is to add "data" or "dataset" to a Google search.
Most government docs have been moved to online formats, and are searchable using Google. However, sometimes it makes sense to search in a more directed way on the government sites themselves, and there are still government documents that are only available in the physical world. These are some links to other libraries' collections and some government sites.
Here are some selected web sources for data. Not every topic will need data, and not all data is findable here. If you need help exploring other sources for data or information, email Jen.