Quotation pages in generally preferred order
Oxford Reference Online: Premium Choice Outstanding site
Bartlett's Familiar Quotations
Literature and Language Reference
The Blue Book of Grammar and Punctuation
Elements of Style — Strunk & White
International Writing Centers Association
Online Writing Lab at Purdue (OWL) Choice Outstanding site
Poets & Writers Online: Resources for Creative Writers
Researchpaper.com Several useful features including an idea generator, extensive collection of pathfinders. Especially useful for undergraduates