Although this section of the OWL website is intended for international students studying in the U.S., the information contained therein is useful for any freshman college student.
Useful items include: the Oxford Dictionary of American Usage and Style; Pocket Fowler's Modern English Usage; A Dictionary of Abbreviations; Oxford Dictionary of English Idioms; and the Oxford Dictionary of Modern Slang.
"About 600,000 words … 3 million quotations … over 1000 years of English. The Oxford English Dictionary (OED) is widely regarded as the accepted authority on the English language."