Public release notes should contain at least:
- release, buildnumber
- all fixed public bugs
- all added public features
QA release notes should contain at least:
- release, buildnumber
- all fixed bugs including bug number
- all added features including links to design docs
Consider your audience and try to think what they need.
An other thing to add is new or discontinued support for certain platforms. (For example we quit support for Win3.1 and added Vista 64 bit).