WebXACT: Homepage analyzer.
MXtoolbox: To doublecheck your the MX-record of your DNS entries.
Apache: Apache 2.2 docs.
Java applets - How to sign a java applet: This is required e.g. if you want your java applet to be able to access your local filesystem.
woorank: A very nice online-tool to analyze your site.
Dan Walmsley: Now to configure the Nginx webserver to run concrete5
Anilcetin.com: Online converter of Apache htaccess-rules to Nginx.
Loadimpact.com: A nice site that provides for free a simple stress-test for your site.
phplens: Performance tuning for PHP & Apache.
gzip-test: Online tool to check if site compression is on.
pingdom tool: Online page speed test.
The Internet Archive: Giant hystorical snapshot of websites.