The linked sites below contain some excellent GED practice tests. The automatic-correction feature allows for quick scoring and indicates problem areas.

Reading: http://highered.mcgraw-hill.com/sites/0809222310/student_view0/ged_practice_test.html

Writing: http://highered.mcgraw-hill.com/sites/0809222280/student_view0/ged_practice_test_pt_i.html

Science: http://highered.mcgraw-hill.com/sites/0809222302/student_view0/ged_practice_test.html

Social Studies: http://highered.mcgraw-hill.com/sites/0809222299/student_view0/ged_practice_test.html