André Carus’s Carnap Blog.

Doug Marshall’s site, including an index of symbols in Carnap’s Syntax, bibliography, and some Carnap texts.

Carnap Collection at the Archives for Scientific Philosophy, Pittsburgh

Carnap Collection at UCLA Library Special Collections

Institute Vienna Circle

Rudolf Carnap, by Mauro Murzi, at the Internet Encyclopedia of Philosophy

Related entries in the Stanford Encyclopedia of Philosophy:

Moritz Schlick Forschungsstelle (preparing the Moritz Schlick Edition)