Your probably better off going with a 9600 GT for a 17" monitor and save yourself $90.00 unless you plan on getting a 22"+ monitor in the near future, your better off going with a a 9600 GT chipset as you prob will be playing in the native 1400X900 or lower res.
Motherboard and GPU: You've got a SLI mbd with an ATI 4850. If you're looking to eventually double up via Crossfire, it won't work. Either go with a Crossfire chipset, Nvidia GPU or a single PCIE mbd
Hard Drive: I tend t seperate my data from my OS, that means a seperate 60-80GB HDD for (I assume) Windows and then another HDD for your data, 250 should do it for MOST. I'm also a redundancy freak so I'd mirror the 250GB HDD but you could do fine running backups to an external HDD.
PSU: I tend to stick with 3 brands, Seasonic, Antec and Enermax. I've only had issues with one Antec PSU and they handled it flawlessy. "If it aint broke, don't fix it"
Case: Why blow $100 on the case with a PSU when (according to your post) you're looking at a seperate PSU? $50 gets you a toolless CoolerMaster Centurion, great airflow and a standard ATX configuration means little worry about the 20+ cable running short.
Misc: I'd also look into additional fans, I tend to run a 120mm in (across the HDDs), a 120mm exhaust and an 80mm blowing onto the CPUs fan. Keep in mind that this is for a mid-tower ATX case, I don't overclock and keep my apt at ~78F so this is more than sufficient.