I have 6 PCs in this room now - 5 of them on 24/7 and at least 2 of them working hard most of the time - so cooling became a real issue this past summer, which has just ended in Australia. I ended up buying a portable refrigerative A/C unit that is set up to blow air across the front of the cases, all of which have an intake fan there. Fans are also placed liberally around the cases, each one has at least 4 chassis fans.
May sound silly but I also paid a bit more for a more efficient processor yesterday, to try to reduce heating and electricity costs. Of course there's probably not much point having a CPU consuming 25 or 30W less than its older brother when the case has 6 hard drives in it.
