) I'll add more to this thread on basic tips for looking after your PC. 
Lets get started with a few simple and quick to do things.
Q. My PCs temps are really high (70c+) what can I do?
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A. Theres a lot of things you can do to keep your PC cool. The first is the most obvious; ensure your case has good airflow. A typical healthy PC will have 1 120mm fan at the front of the case sucking fresh air in while there will be 1 120mm fan at the back of the case to exhaust hot air. Be sure the fans actually have some muscle to them if you want a effective job done. 120mm fans with a CFM of or above 50 are ideal. If your willing to tweak your fans by taking advantage of BIOS settings for fanspeed, then the more CFM a 120mm fan can shift the better.
Q. I've done that, my system is still hot. What can I do now?
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A. More specifically to the above, if your system is still overheating (GPU, CPU, NB, SB) check to make sure dust is not clogging your heatsinks and fans. If you have done that it may be time to add a small 40mm fan to your NB and SB if they are getting hot. However, the most effective way to ensure temperatures never get out of control is to remove any heatsinks covering the NB and SB on your motherbard, as well as any heatsinks that may be used to cover various ICs on the board. Once you have done this clean any thermal paste / pads / gum off of the heatsinks and components and apply some good thermal material in its place. For anything that uses pushpins I recommend Arctic Silver Ceramique. For anything thats just held on with thermal tape, Shinetsu is very good.
Q. My GPU is very hot, what can I do?
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A. Typically, manufacturers set very low fanspeeds, which result in much higher temps that will, of course, over time lead to less lifespan of your components. To remedy this problem remove the HSF from your graphics card, clean any thermal material used and replace with Arctic Silver Ceramique and re-mount the HSF. Note that if the memory for your graphics card is covered by the HSF and uses thermal pads, be sure to remember to place them back over the memory before re-mounting the cooler! With that done, the next step is to increase the fanspeed. On ATi cards you can easily do this via Catalyst Control Centre. Even with stock coolers, you should be able to run 60-80% fanspeed without any significant noise increase. For nVidia cards or if you want one generic application that can OC your card and control fanspeed for ATi and nVidia cards Rivatuner is very good.
Thats it for now. Hopefully that helps some of you look after your puter more effectively.
