These sources are a great place to start because they are easier to use than some of the more subject-specific data archives. Use these if you need data for your assignment, but you do not mind so much about the subject of the data.
These data archives offer more advanced functionality and in-depth data than the introductory archives above. Use these if you are looking for something specific.
Reddit is home to numerous data-centric communities. Feel free to use these to see examples of things you can do with data, as well as discovering new datasets. Some of the content here may be NSFW (not safe for work), so use your judgment as you would with any other social or crowdsource platform.
In addition to these datasets I have listed here, you can also find many more useful examples in another guide prepared for you by our Government Documents Librarian and our Data Resource Management Librarian.