Python is skiing and ruby is snow boarding. One's more fun than the other but they are more similar than different.

If you're tired of the same old ideas, here's a one I don't think I've seen before that I've been planning on trying. Feel free to give it a shot and tell me how it works:
1.) go to Homedepot/lowes & buy tub of mastic sealant from the HVAC isle.
2.) take out motherboard, disks, and power supply
3.) apply mastic liberally to all internal surfaces (making sure to not hide any mounting holes you'll need)
4.) when dry, reassemble computer
5.) apply mastic to external surfaces (metal ones at least)

Mastic dries but retains elasticicty and should provide very good sound dampening. You can apply it with your bare hands and it rinses easily with water as long as you don't let it dry.

I've tried that acoustic foam stuff, and for the results I got I consider it a complete rip off. A small tub of mastic I think costs something shy of 10 dollars.

If you want to take things a step further you could get additional dampening by increasing the mass of the sheet metal case. To do this you could use the wet mastic as glue to attach whatever suitable dense/heavy objects you have lying around. Spare flooring tiles, plywood, drywall, dinner plates. Something acoustically dead would be preferred but probably anything would be helpful. Do not make the mistake of confusing acoustically dead with just plain dead.