Here are three recommended resources:
K12Reader.com has word lists for grades 1 through 5.
Grade Spelling has word lists (and practice games on the computer) for grades 1 through 8 INCLUDING SAT words!
The Basic Cozy Spelling Course is for grades 6 through 8 and has spelling rules, lessons, exercises, dictation exercises, and more.
In addition, be sure to pick up this freebie below: