Warning: You need to double-check the formatting when using all of these tools. They are NOT perfect!
Citation Builders/Generators let you type in your citation (i.e. author, title, journal title, etc.) and generate your citations in a specific style; these work well for citing common items such as books.
Some database vendors offer built in citation generators. When searching in a database, look for words like “Cite Now” or “Cite This” or “Citation Format” because these are links to citation builders. You can find these in databases such as OneSearch, Academic Search Complete, PsycInfo, ABI/Inform, etc.