Quirktools – Screenfly
Interesting site to test mobile web pages of various screen sizes (kindle fire, samsung galaxy tab, google nexus 7, apple ipad 1 – 3 mini, kindle fire HD, motorola razr v3m, motorola razr v8, blackberry 8300, apple iphone 3 & 4, LG optimus S, Samsung galaxy S2, ASUS galaxy 7, apple iphone 5, samsung galaxy s3/s4)
Also this tool offers landscape and portrait modes in addition to scroll & retina effect.
Studiopress – Responsive testing
Responsive test from responsivetest.net
Another interesting tool available online to check web page responsiveness on mobile phones, tablets, laptops and desktops. The web tool has resolutions for testing categorized by devices Apple, Blackberry (Bold 9930, Q10, Torch 9810, Torch 9850, Z10), Samsung, HTC, LG
Other tools
Browser resizing – http://resizemybrowser.com/
Responsive pixel – http://responsivepx.com/
Demonstrating responsive design – http://www.jamus.co.uk/demos/rwd-demonstrations/
Refer Wikipedia for the display of devices by pixel density http://en.wikipedia.org/wiki/List_of_displays_by_pixel_density