Zotero (pronounced 'zoh-TAIR-oh') is a free application and add-on for your browser that can help you keep track of, organize and cite your research.
It allows you to import PDF copies of articles, add notes to what you save and to work collaboratively with others. You should be using Zotero if you are writing a paper, preparing a presentation or doing any kind of research. It will save you time and frustration!