Having helped write some, I think they're da bom.
Seriously,
CSIS is one of the more influential center-right think tanks in Washington, especially in its main area of expertise, international security policy. They are more policy and less political-oriented than the
American Enterprise Institute or
The Heritage Foundation (or, on the center-left, the
Brookings Institution; or, on the libertarian side,
Cato Institute).
Somewhat more to the right politically and ideologically is Frank Gaffney's
Center for Security Policy. CSP is unabashedly in favor of an aggressive approach to international affairs (the Center's motto is "To promote world peace through American strength").
The
Carnegie Endowment for International Peace would be the left-wing version of CSP. Carnegie used to be more center-left, but has become more partisan of late.
Another, newer, organization more focused on the War on Terror is the
Foundation for the Defense of Democracies.