Question: I know of a couple tools to measure end user web site performance and I'm wondering what else is out there. The two major ones I know of are [yslow](http://developer.yahoo.com/yslow) and [Google's page speed](http://code.google.com/speed/page-speed).

Answer: 
Google has another tool within Google Webmaster tools. Go to your site within Webmaster Tools, click on Labs, and then Site Performance. This will show you what Google believes to be your sites overall performance and average load time. It will also list suggestions on what pages are slowing you down. The tool is relatively new and as such isn't great.

Microsoft provides a tool within the SEO Toolkit that is now included in IIS7. When you do a Website Analysis of your site it will tell you how long it took to load each page.
There's a very good metric that never fails for when we tweak (or sometimes un-tweak) our highly successful website. If the pages are even 0.5 of a second slower, sales drop by up to 30%. Sounds crazy, but it's true. When I remember to enable GZip compression and minify our JS/CSS and switched to sprites our sales went up.