How to stress test an apache server running on a linux box
ApacheBenchmark works fairly well and is included in most (if not all) installs of Apache2.
ab -n 1000 -c 5 -C "somecookie=rawr" http://ourwebsite.com/
You can also use Jakarta's Jmeter by Apache.
http://jakarta.apache.org/jmeter/index.html
I used this to stress test my server, and it is quite handy to run from outside computers and workstations with windows, highly configurable, and offers lots of pretty graphs and information especially on failures and what failures return and when the failures happen.
They also of course have Linux builds, but I have not used these.