Firefox.
I got firefox 1.0 installed on both my Windows machine and my Linux machine. It is quite nice.
I got firefox installed properly this time on Linux so that users have permissions to install the plugins.
My favorite plugin is the Mouse Gestures 1.0. I have been using mouse gestures for a year or so, and it is painful to browse the web without them now.
I also install the livelines plugin that interfaces with Bloglines and the JustBlogIt plugin that interfaces with Movable Type.
Everyone should start running Firefox now. There is no reason to run IE. Firefox does all of the good things that IE does, and very few of the bad things (Spyware, Popups etc)
As always, I have a link to firefox in the menu on the right
My employer didn't want firefox installed on my production machine. There is a workaround for this:
Portable Firefox 1.0 (USB Drive-Friendly) :: Mozilla Stuff :: JohnHaller.com