If you wanna add something that will add some speed to your OS and your important applications/games, and if money really isn't that much of an issue, go for a two hard drive setup with a solid state drive as your primary Windows OS drive, and a 7200rpm hard drive like that 2TB Western Digital Caviar Black for storage and games. The WD drives are not all that slow and won't really hurt your games that much at all. This one is a solid choice:
http://www.newegg.com/Product/Produc...82E16822136792
64mb cache, 2TB storage, SATA 6.0 ready and a 5 year warranty. Thats pretty awesome for $149 US.
I just bought this SSD drive for my game rig I'm building:
http://www.newegg.com/Product/Produc...82E16820227706
120GB, and it's been reviewed as one of the better, or best, SSD drive on the market now. There have been some "growing pains" with some people having issues with SSD drives. Firmware updates have made the drives a lot better and less of a problem, but some people still have problems. Whether it's compatability with certain parts not playing nice together, or just a new technology going thru the process of maturing that takes time, who knows. Research the SSD drives before you decide and read all you can about them and get as familiar with them as you can. Then make the best choices for your particular computer build.
Another option you can think about instead of a SSD primary Windows drive is a 10,000rpm WD Raptor drive. They come in sizes from 74GB to 600GB. This is the largest capacity they have:
http://www.newegg.com/Product/Produc...82E16822136803
A 150GB or so would be a good size for a Windows drive with space left over for a few of your really important or favorite programs. A fair amount cheaper too, than the SSD drive.
I hope some of this helps without getting too confusing. Good luck with your rig.
Tom "CC"