sysbench - create high system load

SysBench- the system benchmark is the utility for creating high load on a machine.

So for example with this parameters:
sysbench --max-time=86400 --num-threads=4096 --max-requests=1000000 --thread-stack-size=512 --init-rng=on --validate=on --test=fileio --file-total-size=1024M --file-test-mode=rndwr run you can get a load about 4000, very impressive. So if you ever searched some tool for creating a lot of stress, this one your friend.
See this:
top - 16:26:35 up 1 day, 19 min, 3 users, load average: 7361.45, 7355.47, 735

BTW, the machine was a single processor Intel P4 3.6 GHz with 3GB DDR ECC RAM and Maxtor IDE drive.

(If you ever wanted to know, what the load of a linux system stands for, this link explains it).