Another browser-based tool for viewing the same site at different sizes, but this one displays them all the same time, side by side.
Another browser-based tool for testing your responsive designs at different screen sizes.
Remy created this tool for resizing a viewport to figure out where to put the breakpoints in your media queries.
A handy little service for viewing sites at different dimensions. Just be aware that it doesn’t actually emulate different devices.
A brilliant list of New Year's Resolutions for Coders.