best choice for vid card is the 9800GT, the only one in that list that will come close is the older 320MB 8800GTS. the rest are half as powerful or less.
for your Build a 500-550W PSU will be more than enough.
but for the 20% off, this one would be good:
Newegg.com - OCZ ModXStream Pro OCZ600MXSP 600W ATX12V V2.2 / EPS12V SLI Certified CrossFire Certified Modular Active PFC Power Supply - Power Supplies
20% off deal, plus still take advantage of the Mail In rebate for even less... $56 after 20% Off Promo, & Mail In Rebate... 600W plenty for your system with room to spare, modular PSU, so you don't have to use any extra cables you don't need (means better cable management & room in the case).
as to the hard drives, its because you got a mix mash of drives, one Laptop drive, one external USB drive, and 2 normal desktop drives... laptop drive is much smaller, your going to pay more for less space, the USB external is going to carry a premium just because its an external drive, despite the drive in the case being nothing more than a typical desktop or Laptop drive, depending on the size of the drive (looks like its a 2.5 inch drive, so thats a laptop drive in there)
as to how much space your looking for, its up to you, but what you'll want to look for is an Internal, 3.5", SATAII, 7200RPM Drive, with at least 16MB of Cache memory. use those parameters in your search criteria & you'll be in the right area to be looking...
here you go... to get you started looking in the right direction:
Newegg.com - 3.5", 16MB, 7200 RPM, SATA 3.0Gb/s, Internal Hard Drives, Hard Drives, Computer Hardware
DVD Burners, a DVD Burner will have you covered for...
DVD-ROM
DVD-R & DVD+R (DVD Recording, Record once)
DVD-RW & DVD+RW (DVD ReWritable, Record/ReWrite Multiple Times)
DVD-RAM (Another ReWritable Format, but Slower & intended mainly for System Back-ups or Archiving Data)
DVD+R DL (Also Known As Dual Layer, basically DVD Recording but at nearly Twice the Storage, 8.5GB vs normal 4.7GB)
With All of these you have to make sure the proper media is used for the corresponding Functions.
But the DVD Burners also support all versions of CD Media
CD-R
CD-RW
CD-ROM
so all you do is buy one Burner & its got you completely covered for all DVD & CD Formats.
Most Blu-Ray Burners are the same as well, except they cover Blu-Ray recording & rewrite as well... but considerably more expensive drives & media (25GB and/or 50GB capacities).
I usually look for DVD burners with the fastest DVD Record & DVD Dual Layer speeds.
Lightscribe is something not very useful to me, mainly because its so damned long to burn an image on the disk, takes longer in general to do that than to actually write the data to the disc.
but some people think its cool & comes in handy...
the Lite-on drive supports Lightscribe, the Sony one doesn't. also should note that in order to use lightscribe you have to use special Lightscribe burnable discs...
on to the cases... the links keep timing out for me, won't load, so can't comment on those yet.
hardware
prices 
