RealVNC – Portable VNC Viewer
Real VNC offers a Free edition of their popular VNC Viewer that can be stored and run from a USB device as a "Portable VNC Viewer". VNC or Virtual Network Computing, enables a user to remotely control any machine that is running a VNC Server. Please note that this application DOES save some settings to the system registry. However, the application is a self contained executable and can be launched directly from a portable device on any Windows PC.
Portable VNC Viewer – Real VNC Screenshot
Authors Site: http://realvnc.com/products/free/4.1/index.html
License: Open Source
Download: You can get the RealVNC Free Edition Viewer HERE
Note: Download VNC Free Edition Viewer for Windows "Stand-alone Viewer" zip.