In light of Obama's recent invocation of the states secrets act (see below), a bi-partisan group of Senators have reintroduced a bill which would limit the President's authority in this regard.
“The State Secrets Protection Act will help guide the courts to balance the government’s interests in secrecy with accountability and the rights of citizens to seek judicial redress. The bill does not restrict the Government’s ability to assert the privilege in appropriate cases. In light of the pending cases where this privilege has been invoked, involving issues including torture, rendition and warrantless wiretapping, we can ill-afford to delay consideration of this important legislation. I hope all Senators will join us in supporting this bill.” - Patrick Leahy
via Glenn Greenwald.