For perhaps a different view than Prof. Eugene Volokh's, I offer my old, far-less informed analysis of what the Second Amendment means (Part I, Part II), which was written in response to Glenn Reynolds's 1995 Critical Guide.
The one major change I would make to those posts would be to give much more attention to the federalist interpretation of the Second Amendment, i.e. that it was intended to secure the states against the tyranny of the federal government. After three years of law school (and Fed Soc membership), this now strikes me as far more plausible than it seemed several years ago. It also makes the Court's granting cert to consider a District of Columbia regulation a more interesting case than a challenge to a state law might have been. State regulations of gun ownership could be deemed part of the state's right to decide how its own security is to be ensured, but a federal or D.C. law is more problematic from the federalist perspective. The Question Presented highlights this difference, inasmuch as D.C. isn't a state and thus no resident gun owner could be affiliated with its militia. Justice Thomas's skepticism of incorporation might have forced him to uphold a state law banning handguns, while he can freely strike down a federal/District one.
The source that has informed my most recent (in the past week) thinking about the Second Amendment is Cass Sunstein's TNR review of Mark Tushnet's book Out of Range: Why the Constitution Can't End the Battle Over Guns (Inalienable Rights #03). Sunstein's discussion didn't quite lead me to agree with him, instead inclining me back to the position I had when I first thought about the Second Amendment at all: that it would most properly protect citizen groups that took the responsibility for warehousing arms and training other citizens against the day when tyranny -- whether state, federal or foreign -- threatened.