I'd probably suggest either an Antec Solo (or Antec NSK equivalent) or the P180B (or P180, P182, P182SE, etc).
For a PSU, any Seasonic, or Seasonic-made Corsair would be good (HX520, HX620, VX450, etc).
For HDD, Samsung F1 series, WD3200AAKS, or WD6400AAKS. Samsung SH-S203B or S203N for the DVDRW drive.
Noctua and SilenX fans are also quiet, along with Scythe S-Flex.
As for CPU HSF, either of these would be good...: $59 - Noctua NH-U12P Universal heatsink $57 - Thermalright Ultra 120 eXtreme CPU HS + Scythe S-Flex Fan SFF21E ($15)
Though, the loudest part of a gaming system is most likely the Vidcard (GPU HSF). So, is this a gaming system? If not, you can get a fanless low end card. If it is a gaming system, look for something with a heatpipe, dual slot cooler, if you can't find a fanless (passive heatsink) vidcard.