Over at Salon, legal historian Mark Tushnet writes:
Rehnquist's signature issue as a Supreme Court justice was federalism -- the allocation of some powers to the national government and others to state governments. When he joined the court he was the only justice who cared about limiting Congress' power, and he succeeded in putting the existence of those limits back on the constitutional table. In 1972 the court had only one option when a national law was challenged as being beyond Congress' power under the constitution's "commerce clause": Uphold the law. After Rehnquist, the court has the option of invalidating the law. That's a real achievement.
Whole thing here (sitting through an ad or sub. req.).
I interviewed Tushnet for our July issue. That and other Reason Rehnquistania online here.