Steve describes 14 rules that make up a ‘best practices for speeding up your website’: http://developer.yahoo.com/performance/rules.html

And there’s also a way to use the Firefox add-in, Firebug in combination with YSlow to analyse your sites based on the 14 rules: http://www.getfirebug.com/ and http://developer.yahoo.com/yslow/

We’ve been planning a css/js cache for a while now, but never got it off the ground, still seems that a few of the other rules could provide a good return on little investment.