The Chicago Manual of Style Online is the venerable, time-tested guide to style, usage, and grammar in an accessible online format. It is a reference guide for writers, editors, proofreaders, indexers, copywriters, designers, and publishers, informing the editorial canon with sound, definitive advice. Chicago Notes and Bibliography style (also known as Chicago A) is commonly used in the humanities.
For quick reference for Turabian, take a look at Chicago's contents for Turabian.. Turabian is a simplified presentation of the Chicago Style, and includes great advice for writers at the undergraduate and graduate student levels. The contents of Kate Turabian's A Manual For Writers is available within the Chicago Manual of Style Online, under "Librarian, Teacher, & Student Resources," then "Students." You can also find the print manual in Copley, at the reference desk and on the shelves.
The Purdue Online Writing Lab (OWL) is another great source for quick, online access to citation information in Chicago Style.