Well, how do you define "free"? There are lots of software out there that is "free" but not "open"... Some say "free as in 'freedom'", but freedom from what? Cost? Patents? Usage limits? Distribution limits?
I'll consider gratis as free...
Browser: Without doubt, there is only one that cuts it... I don't care which, but one of the Gecko based browsers.
Text editor: Good old SciTE, spartan but tremendously well made.
Audio player: iTunes or Quintessential, depending on whether I want Apple Lossless or FLAC support. (I've ripped most of my CDs to Apple Lossless)
Media player: VLC for interface and compatibility combination, MPlayer for compatibility with everything
GUI: Much can be said about the various ones for X11 - but I'm certainly impressed by the LiteStep replacement shell for Windows. (Replaces cmd.com or explorer.exe as the GUI shell for Win32 based Windows versions, just like Claris Works did back in the Win16 days)
UNIX: Well, I'd give a word for Microsoft Services for Unix - every other respectable operative system is UNIX in some form or other, but SFU adds UNIX beside Win32 in Windows (instead of on top of, like Cygwin). And who said Microsoft wasn't a UNIX company? I must say that both Darwin and HURD are impressive, though.
Graphics editor: Well, vector graphics would be Expression 3, again a Microsoft product. I've not found a good replacement for Photoshop yet - the GIMP doesn't come close yet.
Graphics viewer: Irfanview
Dev. toolkit: Again, Microsoft. They give all but the Visual Studio IDE away for free, and the IDE can be replaced. GCC lacks in optimisation compared to the Microsoft C Toolkit, but it's a competitor of rank.
Scripting environment: Well, I could have Spidermonkey here, or Python, or .NET, or Mono. But really, parrot got to be the coolest one out there - it'll eventually be able to run PERL5, PERL6, Ruby, PHP, Python, Forth, Scheme and likely also ECMAScript on one bytecode engine - and be faster than the CLR (.NET, Mono) and JRE and maybe even the current bytecode engines for given languages.
And, finally, coolest game: Zig
(Oh, I forgot - that's not the coolest free game, just the coolest non-rip-off game. The title of actual coolest free game would be Beneath a Steel Sky, which Revolution released to the ScummVM
developers. You wouldn't believe how long it took me to figure out how to get into the underground when I first played it, back when a CD drive for a PC was state-of-the-art.)