Screenqueri.es is an awesome website where you can test your responsive web design using using pre-defined device sizes, or drag the screen handles to change the view window to any size you want.
Naturally, tools like this aren’t a complete replacement for testing on actual devices, but Screenqueri.es is helpful for testing devices you don’t actually have access to. It can be used to view both live websites, and localhost addresses. Below is the Stem website, viewed with the same screen size as the Kindle Fire — I never tested with this screen size when developing the website, and didn’t realize how cramped the logo looks:
Right now my responsive web design testing technique combines the devices I do have, some emulators, and, as of this week, Screenqueri.es. What tools do you use when the devices you need to test aren’t handy?