I ended up getting the Scythe Ninja CPU cooler today — only a couple of places in Australia seem to sell them, but as luck would have it, one of them was open, and in the city. I had to head in to the city anyway, so I grabbed one this morning, and spent a couple of hours ripping the guts out of my PC to install it.
The Ninja is on the left, of course, with the stock Intel cooler from my Core 2 Duo sitting beside it. There’s no fixed fan on it, but it comes with a 120mm fan and clips that you can use to attach it to its side, blowing air through it rather than down on to it.
The results are fantastic: I’ve left my motherboard thermal-controlling the fan, but it barely hits 1000rpm when both cores are flat-out, with the CPU temperature barely hitting 40 degrees. There’s a faint whirr from the video card cooler, but apart from that, the box is basically silent now when the hard drives are idle. There’s not much I can do about the hard drives though, so for now, I’ve got a PC that’s about as quiet as it’s going to get.