Well we've had some good ideas so far, thought I think we can combine the above suggestions into one.
~ You get a 5770 over a GTS 450.
~ Includes keyboard & mouse as well.
~ Comes with a much nicer NZXT case.
All before a $15 rebate which should cover shipping.
For the headset I would shop around because its something that you want to make sure is comfortable. I suggest Sennheiser or Beyerdynamic if you want quality, however they can be expensive.
EDIT: Or you can go for the Keyboard/Mouse/Combo ScrewySqrl posted if your OK with speakers.