Zotero is probably the best current tool for managing larger amounts of sources. Zotero is a cloud-based (you can access your sources across devices), browser plug-in that allows you to collect, organize, cite and share your research sources. It can gather your sources and work inside Word or Google Document pages to create references and bibliographies in your chosen citation style. Note: there is a bit of a learning curve to using this tool effectively, so plan ahead! Zotero Help or Learn to Use Zotero in 30 Minutes (video).
To quickly generate a single reference or short bibliography, try ZoteroBib.
Lastly, a great tool for note-taking and gathering and comparing multiple sources is a synthesis matrix. At it's core it is a spreadsheet with notes for each source based around common themes. Here is an example synthesis matrix (Empire login may be req'd)
