The New RefWorks (Version 3) offers a well-designed interface and many new features.
For specific style guides, choose one of the tabs at the top of this guide:
Humanities - (MLA, Chicago, Turabian, SBL, Notes)
Social Sciences - (APA, Chicago, Turabian, AAA, legal & government documents)
Sciences - (APA, ACS, AIP, AMA, CSE, GSA)
Images - works of art, photos, etc.
Audio & Video - music, film, etc.
Citing Sources (Duke University)
Includes instructions and examples for five major styles (MLA, Turabian, APA, Chicago, and CSE).
The Jacobson Center for Writing, Teaching and Learning offers individual help with writing and also this useful guide:
Writing Papers: A Handbook for Students at Smith College
Read "When to Cite" starting on page 47 (pg.54 of 71 in pdf file).