Being web application developer, over 10 years. I was involved in so many external and internal website development. I would be documenting all my web page performance improvements and tools I have used.
http://developer.yahoo.com/yslow/matrix/ - This are some of the best practices from Yahoo web team. They tool called Yslow which records real time performance and gives the grading for the sites. A to F. A and B being extremely good.
Fiddler - IE plug in to view all the HTTP request.
YSLow - Yahoo tool for Firefox plug for all page performance.
Page Load - http://code.google.com/speed/page-speed/index.html
Asp.net - performance improvements .