Don't go with Marbury v. Madison. The older the cases are, the harder the langugage is to read (plus, it was such a major landmark case, essentially establishing the Supreme Court's ability to review acts of Congress, that almost certainly someone else will work on it. Plus, the material will be like wading through the ocean). Here's a suggestion:
Korematsu v. US (1944) - The Court basically stated that it was legal to hold Japanese immigrants indefinitely in concentration camps because they posed a threat during WWII. The case took place in California, and since slavery, it's probably been one of the worst cases for civil rights in US history.
And if you don't like that, just check out the Landmark Supreme Court Case website. It'll help you find something you might be more interested in.