browser based speed profiling tool from Google

remote monitoring service for websites... free for "personal" package (checking every 8 hours)

Very nice looking diff tool for Mac.

www.sendmoneypacific.org has been created through the joint Australian and New Zealand Governments' led initiative 'Reducing the Cost of Remittances to the Pacific'.
The website provides important information on the many choices migrants living in Australia and New Zealand have when sending money back to their families and friends in the South Pacific island nations.

Nice interactive CSS3 generator.

This checker performs various tests on a Web Page to determine its level of mobile-friendliness

task list

online task list, timer, performance analysis ("for programmers")

JS library to allow CSS to conditionally set styles based on browser support for modern features like canvas, border-radius, etc.

Firebug for IE, Opera, Safari.

Standalone full set of IE browsers

app to run multiple versions of IE concurrently for testing

Velocity - check bandwidth

comprehensive test of primary and secondary DNS for a domain