Free Mobile Performance Testing with Akamai's Mobitest
Test your website performance on a mobile device
Mobile Emulators and Simulators - The ultimate guide to mobile developers | Breaking the Mobile Web
Links to all the available mobile emulators!
Screenqueri.es | Pixel Perfect Responsive Design Testing Tool
Sweet
WebPagetest - Website Performance and Optimization Test
ProtoFluid - HTML5 and CSS3 Web App Prototyping
Test your @media queries and web app on various screen sizes