Is there any complete Ubuntu server hardening document which will suffice ISO 27001 or PCI DSS or any other security standard.
I don't know of any official ubuntu server hardening document, but hopefully the following will give you a good starting point:
NIST (National Institute of Standards and Technology) publishes guidelines on how to secure *nix systems. This is what the big boys use as a starting point (DOD, Army, Etc.).
You can use tools like Nessus, OpenVAS, and other vulnerability scanners to give you an idea of what ports and services need to be shut down, as well.
The National Vulernability Database is a good site to cross reference your software configuration against, as well.
If you are trying for compliance with ISO 27001, Then ISO should have documentation and checklist for this sort of thing (although it's a B*tch to look through).
Sorry if this is too general, I hope it helps.
The above answer is a great one, but my only personal preference is the CIS Debian Hardening Guide that can be found at: http://benchmarks.cisecurity.org/en-us/?route=downloads.show.single.debian.100