foxit software has one of my must have installations after the many installs and upgrades i've done of windows 7 over the past year.  i typically have occasional need to open a pdf file, and foxit reader does that job well, but what i really like is the ifilter for searching for the correct pdf to open and more recently (thanks to dan orum for this) tim heuer's pdf preview handler (with foxit software sponsorship and license).