You are going to want to scrap the Rosewill PSU in short order. They are not a very reliable brand. You won't want your $200 graphics card fried.
Look for corsair, a 750TX would be suitable. Alternatively PC Power and Cooling or Enermax.
Try an Antec 300 for a well regarded, low cost case. General cases are personal preferance - have a look at what other people in the forum go for and what you can afford.
Honestly I think that the 955 is a waste of money. Going with the 940 will save you $80 and it will have almost identical performance. If you want the same performance out of it you can do a light OC of the Bus speed (this is the only difference between the cores of the two processors, the 955 uses the same cores and overclocks to the same speeds as the 940). A DDR3 memory controller isn't worth it IMO, especially since there are no tangible performance gains with DDR3 over DDR2.