Let me first off say - I love Macs. The only reason I have not converted to a Mac is because I am a poor uni student.
It is because of this same reason that I have searched around the net for great that allows me to focus on my work.
Oh, and the necessary requirement for me is that it must be free 
The 'Make windows suck less' list
VirutaWin - Virtual Desktop Management.Fiddling with tens of windows? Categorize your apps by associating them with virtual desktops.
Launchy - Application launcher. Similar to Quicksilver.
Thunderbird & Firefox - Browser. One of the first to introduce tab browsing. I'm sold.
BitMeter - Network Traffic Monitor. Small but powerful app. Also has transparently and click through.
CLCL - is clipboard caching utility (multiple clipboard entries).
Feel free to edit and add any free software that you find hard to separate with.