First and foremost:
Welcome to SPCR!
If you have some airflow through your case, then the Zalman passive northbridge heatsinks work well. If you have room, you might even consider the larger variation: Zalman ZM-NBF47
Replacing the northbridge fan (small, high speed, noisy and failure-prone) with a passive Zalman was one of my four best cooling and quieting mods.
The other three:
- Replace VGA fan with passive Aerocool VM-101
- Replace Antec PSU with Seasonic S12-430
- Replace CPU heatsink, first with fan-modded Zalman 7000, then a Thermalright XP-120 with Papst fan