I like use Sumatra PDF, because it is a slim, free, open-source PDF reader for Windows. Portable out of the box. and I just notice it has updated to 1.3 on Feb 04, 2011 with many changes,
* improved text selection and copying. We now mimic the way a browser or Adobe Reader works: just select text with mouse and use Ctrl-C to copy it to a clipboard
* Shift+Left Mouse now scrolls the document, Ctrl+Left mouse still creates a rectangular selection (for copying images)
* ‘c’ shortcut toggles continuous mode
* ‘+’ / ‘*’ on the numeric keyboard now do zoom and rotation
* added toolbar icons for Fit Page and Fit Width and updated the look of toolbar icons
* add support for back/forward mouse buttons for back/forward navigation
* 1.2 introduces a new full screen mode and made it the default full screen mode. Old mode was still available but not easily discoverable. We’ve added View/Presentation menu item for new full screen mode and View/Fullscreen menu item for the old full screen mode, to make it more discoverable
* new, improved installer
* improved zoom performance (zooming to 6400% no longer crashes)
* text find uses less memory
* further printing improvements
* translation updates
* updated to latest mupdf for misc bugfixes and improvements
* use libjpeg-turbo library instead of libjpeg, for faster decoding of some PDFs
* updated openjpeg library to version 1.4 and freetype to version 2.4.4
* fixed 2 integer overflows reported by Stefan Cornelius from Secunia Research