stock HS is fine unless ur ocing, which u dont need to.
HD, get a 80 or 160 gb sata (i recommend seagate, they are silent as hell)
PSU, u can get anything between 420 and up. If ur gona oc, u need strong rails, but dont worry about that.
OCZ, thermaltake, and other brands make good psus
modem, mobo should have integrated
My current specs:
Biostar TPower x58
XFI GTX260 Black Edition
640 WD Caviar Black
Vista Home Premium x64