Free reading worksheets appear online at ReadWorks.org and similar sites. This website provides unlimited free reading passages and matching question sets based on certain skill and strategy sets for students of all grade levels.
SuperTeacherWorksheets.com is a membership-based website that also has a few free reading comprehension worksheets.
Education.com provides a limited amount of free reading worksheets without a membership for students from kindergarten through 12th grade. Teach-nology.com provides a limited amount of free reading worksheets without a membership for elementary grades under Language Arts and Reading Comprehension.
Finally, ABCteach.com provides a free membership with access to free reading worksheet downloads.