Test your media query based designs on a variety of devices, including phones, tablets, computer monitors and TV sets.
Screenfly by QuirkTools is perhaps one of the most straightforward responsive design emulator with a choice of 25 devices and screen sizes, including 5 kinds of tablets.
Others:
Responsivepx: http://responsivepx.com
ProtoFluid: http://app.protofluid.com
Edible Vineyard
Great example of responsive web design, where the layout isn’t dictated by wanting to be responsive.
The different layouts at varying sizes all work individually.
