Thawk,
Hmm, well I would say that it all depends on how much green stuff you are willing to spend.
You new componenets look real nice, and should be very fast. A 15GB hard drive, though plenty of space for most things, is starting to be on the small side nowadays - especially if you have broadband and download alot or if you do lots of things with audio and video.
If size is not a concern, remember that the hard disk is one of the primary bottlenecks for dekstop systems nowadays. How old is your current hard disk? If it is a couple years old and you have the cash I'd say you would definitely see a performance increase if you bought a new new one. A newer 7200 RPM disk will yield better throughput so you'll be able to take advantage of the ATA100 controller on your new motherboard and, more importantly, it'll have lower random acess times so your system will just feel a bit snappier and faster (programs will start quciker and such). NewEgg.com is a great place for new hardware. I would personally recommend the IBM 60GXP series, they are moderately priced, reliable, have very good performance, and come in farily diverse range of capcities to suit your needs.
Hope that helps a bit and good luck,
obispo21