Can't right now, as apparently my home internet connection is down. Off the top of my head tho, basically I used python's random module, and got a random int, and a random float, then did a bunch of pow(rfloat, rint) and multiplications in loops and bit shifts and so on. Basically i tried to utilize all the parts of the CPU I could think of, and keep the cpu usage pegged.
Better yet:
apt-get install cpuburn
Alternatively, you could use Prime95. Run it in stress test mode and it should heat your room just fine.