Google Dictionary - Use the "define: x" feature. Where "x" is the word you wish to define.
Dictionary & Thesaurus - Merriam-Webster Online
Thesaurus - An Ask.com service
Visual Thesaurus - The coolest thesaurus ever!
EasyBib - Free bibliography creator.
Son of Citation Machine - You enter the information, it creates the citation.
GoogleDocs - Like Microsoft Word and Excel, only online and free.
SparkNotes - It's not cheating, it's using every resource you have available! Use this website for study and review purposes.
ReadTheWords - If it's in a digital format, this website can read it to you aloud for free. Registration is required.