I don't promote standardized testing and I would generally discourage parents from relying on them, but we've had a couple of instances in our house where the kids were curious about the whole standardized test issue and I've pulled samples off the web to show them what people are talking about. Last year my daughter actually spent a couple of days taking some reading comprehension tests. She was curious about the whole test-taking process and wanted to know where she would fall according to her "grade level" even though we don't focus on grade-levels in our house. It was enough to satisfy her curiosity.
These links were posted via one of my local homeschool email loops. They are test prep sites from the New York State Regents. I'm sure there are many more like them, but they do appear to be free and cover every grade level and subject.
Elementary Test Prep
High School Test Prep
Thanks, Priscilla and Rebecca, for the links.