The NZXT Duet is very nice. I like it because it allows for full size ATX w/ good psu. Has good cooling and is very, very plain (not a lot of crap on it). Front USB/Audio/IEEE1394 and a fold down front panel for drives.
The stock fans in the rear are quite loud, I'd invest in more quiet fans for the exhaust.
It comes with one fan and a memory card reader. It has a internal slot for the MS MCE remote receiver. It also has a LCD that show fan speed and temp. but I don't use it
I don't know if a 6800 will fit because the hard drive cage is right behind where the GPU goes. It does fit a 6600gt with room to spare. If you want I can measure and see if it will fit, just post how long your card is.
Note: the receiver PCB has to be taken out the casing(and the bracket they give has to be covered with tape) and the bezel has to be taken of the DVD drive