Free and open (to anyone, not contingent on UF affiliation):
Zotero - free downloadable Firefox extension that enables single-click addition of items of all sorts (PDS, images, audio, videos, journal articles) to your personal library. Guide to Zotero from University of Washington Health Sciences Library.
Citeulike - "Join" to discover new resources, receive automated article recommendations, share references with peers, store and search your PDFs and store references found online.
Mendeley - free tool to generate citations and bibliographies, highlight and add sticky notes to PDFs, access papers from anywhere online, import papers from other research software, find and securely share relevant papers. Guide to Mendeley from University of Washington Health Sciences Library.
EndNote Web (info on tool at link but to register/use, follow UF Health Science Center Library Databases-QuickPicks grid's Web of Science or alphabetic link to Web of Knowledge. Web based so available from any computer. Must register on campus but free to UF faculty, staff and students. More limited in # of styles available than desktop EndNote. See Help page for more information.
RefWorks (info on tool at link, but to register/use, follow UF Health Science Center Library Databases and R in alphabetic list to RefWorks.) Free to all UF faculty, staff and students. Must register on campus, then can use off campus. Import citations from databases or links from webpages and share. Fewer bibliographic styles than EndNote desktop and needs proofreading and editing more often. Online tutorials, user manual and online training schedule available from producer.
EndNote & RefWorks Tutorials from Yale University Library. Tips on importing results into EndNote and RefWorks (some dated.)
EndNote - software isn't free but UF librarians' classes every semester are. Librarians also answer questions for UF faculty/students/staff on this software through Ask A Reference Question . Producer has released new version every autumn for several years (Version X6 new as of Fall 2012). Significant student discount available through UF Bookstore or directly from producer.
AMA Style Guide - concise, tabular form from University of Washington Health Sciences Library. 10th edition AMA and blog, AMA Style Insider. Purdue University's Online Writing Lab's brief AMA guide has an overview and separate page (navigate in left sidebar) for print and electronic sources.
APA Style Guides - concise, tabular from from University of Washington's Health Sciences Library.University of Illinois , Purdue University's Online Writing Lab (last reflects the latest--7th--edition) or Purdue University Global's Apps and Extensions to Help You with APA Citations.
Vancouver Style Guides - Detailed with examples from University of Western Australia and Murdoch University (also in Western Australia) , University of St. Augustine for Health Sciences, PDF with examples from Imperial College of London.
NCBI Style Guide comprehensive and easy-to-use digital style guide divided into two parts: tips for general writing and tips for the biotechnology field. Part I includes guidelines for grammar, punctuation, and style that will be helpful to writers in any field, with notes on "Wordy Constructions to Avoid" and "Voice: Active versus Passive." Part II outlines disciplinary conventions in biotechnology with special attention to writing for web pages.
Legal Citations (includes cases and regulations) from U Mass Amherst
Basic Statutory Citation from The Blue Book, hosted by Georgetown University's Law Library