<p>Looking for links to resources that will help me write a user guide for a software application. I'm after something that will help me to structure my guide, give it an appropriate writing style, and ensure that it has an excellent look and feel throughout. </p>

This link has some strong points. Each point is presented with clear speech and with inline justifications.
When writing procedures, use the
  active voice (e.g. Click this) and
  address users directly (write "you"
  rather than "the user").
When explaining an action, use the
  "command" form of the verb:
"Choose an option from the menu and
  press [ENTER]."
http://www.klariti.com/technical-writing/User-Guides-Tutorial.shtml
Here is the complete list of the topics covered on the aforementioned article:
Front Page (cover pages)
Cover and Title Page
Disclaimer
Preface
Contents
Body of the guide
Procedures
Writing procedures
Chunking text
Number your steps
Using the If-Then Approach
Reference Materials
Back Matter
Glossary
Index
Establishing Standards
Document Format
Structure Style
Technical Language
Addressing the User
Presenting your material
Special Requirements