Read a great article about High Performace Web Site secrets on Skrentablog, called 14 rules for fast web pages. The list provided there is highly accurate and up-to-date.

List for Fast Web Pages

1. Make fewer HTTP requests - Reducing 304 requests with Cache-Control Headers
2. Use a CDN
3. Use a customized php.ini - Creating and using a custom PHP.ini
4. Add an Expires header - Caching with mod_expires on Apache
5. Gzip components
6. Put CSS at the top in head
7. Move Javascript to the bottom
8. Avoid CSS expressions, keep it simple
9. Make CSS and unobtrusive Javascript as external files not inline
10. Reduce DNS lookups - Use Static IP address, use a subdomain with static IP address for static content.
11. Minimize Javascript - Refactor the code, compress with dojo
12. Avoid external redirects - Use internal redirection with mod_rewrite, The correct way to redirect with 301
13. Turn off ETags - Prevent Caching with htaccess
14. Make AJAX cacheable and small

Sources & References

The full talk has details on what all of these mean in practice.

• High Performance Web Sites: Rough Cuts Version
• Rules for High Performance Web Sites
• Image maps
• Speedy Sites with Image Sprites and CSS, CSS Sprites: Image Slicing's Kiss of Death
• inline images: The “data” URL scheme
• The JavaScript Minifier
• Dojo ShrinkSafe
• 10 Status Code Definitions, All 57 Status Codes
• IBM Page Detailer
• Firebug
• Performance Research, Part 1: What the 80/20 Rule Tells Us about Reducing HTTP Requests
• Performance Research, Part 2: Browser Cache Usage - Exposed!
• Performance Research, Part 3: When the Cookie Crumbles
• Performance Research, Part 4: Maximizing Parallel Downloads in the Carpool Lane
• High Performance Web Sites: The Importance of Front-End Performance
• High Performance Web Sites: Rule 1 - Make Fewer HTTP Requests

Recommendations

I recommend the article Speed Up Sites with htaccess caching to reduce the number of HTTP Requests. I also recommend hosting your static cacheable files on a separate subdomain, like s.askapache.net instead of www.askapache.com. You will also need to implement a version control system using mod_rewrite.