The US Courts Website now has a series of podcasts on landmark cases by the US Supreme Court which have shaped our history and continue to affect American political and legal life. Each podcast briefly discusses a different case with a law professor. The case's background is explained, the key arguments summarized, the ultimate decision is discussed, with comments on why the case remains relevant today.
Thus far, two podcasts are up, one on Mapp v Ohio (1961), and another on Texas v. Johnson (1989). More podcasts will be added in the coming months. An excellent resource, and you can download the podcasts and get them on your iPod.