The answer to your question is Yes, there are addresses which work like what we call private addresses in IPv4. They are called Unique local addresses in IPv6 and have a special prefix of FD00::/8. They can even be “inofficially” registered at http://www.sixxs.net/tools/grh/ula, which should help to prevent from choosing an address space which is used already by someone else. The rules are the same like for private addresses. ULA’s as they are called should never be routed to the Internet.

It is important to make clear that this is a replacement for private addresses but NAT’s is a concept that should not be used in an IPv6 network. So the idea behind the whole thing is that you could use ULAs for addressing all your internal systems, which means they are not reachable from the Internet per se. And then only assign public IPv6 addresses to interfaces of hosts that need access to the Internet. And only corporate service or application systems that need to be accessed from the Internet and are in the DMZ get a public IPv6 address.

Cool stuff, isn’t it?
Hope this helps
Silvia