I run two 21 inch monitors at 1680×1050 and the theme I’m using is responsive. I went looking for an easy way to see how my site looks on different resolutions and devices. ,these three sites fit the bill.  I use the wordpress plugin WPtouch which detects phone and tablets and reformats my site to better display and function on them.

The sites below only show you the resolution of each device not the mobile version

CyberCrab

http://responsivetesttool.com/

Screenfly

http://quirktools.com/screenfly/

Do you know of any better sites to do this?