My 2cents
Wow - so many windows users visit this forum!
I guess I'll throw my pennies into the pot here. My setups change almost every day, so tomorrow the a,b,c list will not resemble today's. Oh well. I currently have three machines, working. I have others, broken. That also changes daily. Today the three working computers happen to have:
a) FreeBSD-9-STABLE/ X windows alone
b) Haiku-OS/ Haiku Desktop
c) FreeBSD-2.2/ WindowMaker