Colorín Colorado has a wealth of resources that will help you in planning instruction for your ESL students. The "For Educators" section includes information on many topics, including assessment, literacy instruction, and content area teaching. Be sure to check out our "Web Resources," which will take you to some great articles and online resources.
The Reading Rockets website also has lots of useful information for ESL teachers. In "Articles from A-Z," there is a section on English language learners where you can download a variety of articles. You might also want to explore the TESOL (Teachers of English to Speakers of Other Languages website). In the "Emerging Teachers" section, there is a feature called Teaching English as a Foreign Language: Questions and Answers, which uses a question-and-answer format to present information on teaching specific skills, planning lessons, and many other topics of interest to ESL teachers.