This site is really impressive! The author Dave Bunell is editor of the NSS News and a really good cave photographer.
Even better than his show cave pages is the virtual cave with its extraordinary photographs.
The national organization where all grottos (american for caving clubs) and cavers find their home.
The NSS News is a very interesting publication, and their online bookstore sells numerous interesting speleological books.
The NSS is involved in cave protection and organizes an annual Convention.
a non-profit organization of publicly and privately owned show caves in the USA.
The list of caves contains only organized show caves, so many nice caves are not included.
They have a cave board with many interesting postings.
The traffic on the board is rather low, but its still a good resource.
This is a list of the longest and deepest caves of the USA.
Be aware that most of the caves are not accessible to the public.