A + Guide to Research Papers -- Step-by-step instructions and advice on writing your paper.
Creative Writer Games -- Games to inspire you with your writing
Grammar Bytes! Interactive Grammar Review -- Like the title says, it's an interactive grammar review.
Grammar Girl - Quick and dirty tricks for better writing
Grammarly - Proofread your writing for grammar and punctuation mistakes, avoid plagiarism and find better word choices.
Guide to Grammar and Writing -- Complete information on grammar, punctuation, and essay writing, plus links to other good sites.
OneLook Dictionaries -- Search over 500 dictionaries all at once.
PaperRater.com -- Free service that provides grammar checking, plagiarism detection and writing suggestions.
Purdue University On-Line Writing Lab -- Links to writing resources at Purdue and elsewhere.
Reference.com -- Dictionary, thesaurus, quotes, and translator covering over 50 languages.
Synonym finder - Stop using the same word over and over
TypeIt - Type diacritics and foreign characters from 21 languages and then cut and paste them into your document.