This entry on MSDN (Microsoft Developer Network) is a good piece on the basics of web performance engineering. While reviewing the steps covered in the article I discovered that one of my Apache servers had KeepAlives disabled, it appears that the default value for this has changed from ‘On’ to ‘Off’. The performance improvement was immediate and obvious.
It discusses several basic concepts including TCP settings, web server options and to a lesser degree client side methods for improving web page load times. It also explains the use of a free tool available from Microsoft (imagine that – something free from Microsoft!); Visual Round Trip Analyzer. I am downloading it as I type this.