Of course campaign finance and the Second Amendment have been the big winners. As I noted yesterday, abortion used to be a hot topic but it's only had one mention thus far (from Senator Hatch).
But we've had questions about the prohibition of establishments of religion (Senator Feinstein), the Sixth Amendment right to confront witnesses (Senator Klobuchar), the Constitution's restriction of federal courts' jurisdiction to "cases and controversies"--called "standing" in legalspeak (Senator Feinstein); the First Amendment, in particular limitations on libel claims and the recent Supreme Court case dealing with animal "crush" videos; and the Takings Clause, which requires the government to pay just compensation for any property taken for a public purpose (Senator Grassley).
Senator Grassley then went on to ask about the Court's authority with respect to state laws defining marriage, asking Kagan a question that he asked Justice Sotomayor last year about a 1972 decision in which the Court found "no substantial federal question" in a case challenging a state marriage law. As Kagan pointed out, because that decision was not a ruling by the Court after hearing the case on the merits, but was made at the preliminary, jurisdictional stage, it probably is entitled to less precedential effect than a merits decision. Kagan said that, but Senator Grassley was unhappy with that response. Chairman Leahy jumped in to say that Kagan's response was "hornbook law" (legalspeak for a well-established principle).
Senator Specter took this kind of question to a different level, asking Kagan whether she would vote to grant certiorari (legalspeak for granting review by the Supreme Court) of several different legal issues, including one presented in a pending case. Kagan of course refused to answer: that would prejudge questions about whether to grant review that she will have to decide if she is confirmed.