ABCTeach
Click on Reading Comprehension and then Grade Level

Brain Child
Slow but worth the wait.

Florida Testing
Designed for Florida, but good practice. Click on the picture of the cat, click "Next", then click "Practice Tests".
Can practice writing too since some of the questions also involve writing a paragraph.

The Mental Edge
Excellent practice but it loads VERY SLOWLY. Be patient (count to 100).

Illinois Standard Achievement Test
I know we don't live in Illinois, but these tests are in SAT format. They have practice tests for grades 3, 5 and 8 in reading, writing and math and for grades 4 and 7 in social studies and science. Just go to the samples. This even scores them for you. This one loads slow too.

Grammar
Click on the word "quizzes" somewhere between the ads at the top. Some of this is above elementary level so choose what you can use.

BrainTeasers
Brain Teasers for different grades levels--a new one posted each Wednesday. Check out the "Archives" for 3 more.