You can find useful worksheets in the following places:

BBC Learning English For Teachers
Worksheets and teaching ideas for many of the BBC Learning English sections.  New resources are regularly added to this great site.

Developing Teachers
Lesson plans, including lesson plans for specific days of the year, teaching tips and much more.

British Council Teaching English
Long list of lesson plans on a variety of interesting themes.  Many of the lessons have downloadable audio files.

Jamie Keddie
Tips and lesson plans from Barcelona’s most exciting tefl teacher

Tefl clips
Lesson plans based around youtube clips