I started to use Zotero - a Firefox plugin - to manage numerous categories of academic papers, books and their bibliographic information, and it was soooo amazing! By just clicking a small button at the end of the address bar, you can easily import the link of an article from various online sources and databases, like JSTOR, ScienceDirect, Google Books, Amazon and so on, and its citation information is also automatically loaded.
When you are writing an article, it is also very easy to create a list of references using Zotero. For instance, if you are using the Word processor, all you need to do is to highlight the list of papers you want to cite in your Zotero window and drag them onto the Word file you are using. Different citation styles are also available to be chosen.
You can also easily creat groups, share your libraries with friends and colleagues, and synchronize all your library information if you are invited to some other groups.
Hat tip to Todd.