English File (Oxford University Press) - Grammar, vocabulary, and pronunciation lessons at all levels of expertise
OER Commons Community College ESL Resources - Freely available textbooks and other educational materials
Cool Websites for ESL Students (UIC Tutorium) - List of ESL web sites compiled by a university tutoring center
Simple English Wikipedia - Wikipedia articles written in an easy-to-read style
BBC Learning English - Free audio, video, and text resources for English language learners
Merriam-Webster - Exceptionally high-quality dictionary. Definitions include audio pronunciations.
Google Translate - Translate web sites and documents in dozens of languages