OK, if it is for general gamig.(opinions might be diferent, this is my opinion)
If you are using Vista, i would go with more memory (just in case)
Psu i would go with a 650w or 700.
Gpu well many opinions on this one, all depends on your budget.8800 gts and up, 265 or 280, ofcourse all depnds on your budget.I also know there are people that say (for MFS the Ati is a no(i dont know why)).
For MB read this it might give you a general idea
http://techreport.com/articles.x/17598.
For a case well there are so many but has long you see it has good "room" any will be ok (i guess its the better advice, since you want to buy the PSU in separated the rest is just stetic and budget).
For HD look into Western Digital or Samsung and choose the best one that fits your budget.
Hope it helped, all depends on your budget for a more peculiar advice.
keeps us informed