Hi, as a matter of fact there is such a thing...
http://eshop.macsales.com/item/NewerTech/VIDU2DVIA/
Features
Works on PC and Intel Mac models
Lossless compression
LCD, CRT, projector displays
Connect one extra monitor per adapter to your desktop or laptop's USB port!
Configure connected monitors to either clone your primary screen, or extend the desktop allowing visibility of more applications at the same time!
Display Modes:
Can easily Mirror the main display
Extend left, right, above, or below
Can be rotated left, right, or upside-down
Windows Vista & 7 Aero support
Windows XP and Vista 32-bit support
Standard and Widescreen ratio aspects
High-Performance DDR memory
Completely silent operation
Uses very little computer resources and offers a vast array of screen resolutions and color depths ensuring little performance difference between a screen directly connected or via USB 2.0
Supports resolutions up to 2048 x 1152 including SDTV/HDTV resolutions: 480i/p (640x480), 720p (1280x720), 1080i/p (1920x1080)
There may also be an Apple adapter, but they change Video ports more often than I can keep track of. 😉