Perhaps any spare money can be spent on a quieter cooling solution. My experience is that stock coolers aren't the quietest beasts around, nor do they have the best cooling performance.

Rigging your CPU with a better heatsink/fan combo not only reduces the noise output from your system, but also allows you to overclock your processor further. Thus, enabling better performance indirectly.

Quieter case fans and fan controllers are great ideas, as well.