The Busy Teacher website is a great source of free printable ESL worksheets and lesson plans for Busy English Teachers. BusyTeacher.org is a place where teachers can share their printable ESL worksheets, ESL lesson plans and ideas for lesson activities with other teachers for free.
The first and busiest section of the site lists Lesson plans, clearly categorised and divided according to level and skill area. There are worksheets covering grammar, vocabulary, speaking, reading, listening, writing and pronunciation lessons. One nice touch is the 'Seasonal' section which lists lesson plans according to the month. February, for example, includes lesson plans based on Valentines Day.
There is also an ESL Articles area, containing a lot of articles of interest to ESL teachers. If you haven't come across this site before, take a look at it today.