For independent, self-checking comprehension practice, I highly recommend Test Tutor.
Several excellent short, interactive reading selections which stress a specific reading skill. Go to grade level and click on a lesson.
20 Best Reading Strategies
20 strats, broken down step-by-step.
Reading comprehension passages about various topics.
Florida Skills Practice: Reading
Short animated lessons with assessments built in.
Inferring and Other Skills
Great break-down of reading skills, one per page.
Interactive Reading Comp Grade 5
Although for grade 5, this mixed collection of reading samples is an excellent interactive practice for fourth graders.
Online Practice Reading Tests
Stories and multiple choice answers.
Reading Comprehension - Free Worksheets
Great selections for teachers with related questions and activities.
Texas Online Assessment
Stories and questions for online practice.
Reading Comprehension Practice
Space and planet related comprehension and English skills.
A number of strategies for before, during, and after reading.
A number of interactive sites covering all areas of reading comprehension.
Texas End of Year Reading Test
2004 test to be completed online.