Also noteworthy is Tsung[0], which is (far) more complicated but can speak more protocols, be configured to emulate user behaviour a little more closely and send crazy amounts of traffic.
Tsung also has the interesting property of modeling traffic as individual user sessions, with probabilistic thinktimes and dynamic variables. Makes it possible to test your app in a much more realistic way than most tools, which just benchmark a series of identical requests or replay a log.
Also noteworthy is Tsung[0], which is (far) more complicated but can speak more protocols, be configured to emulate user behaviour a little more closely and send crazy amounts of traffic.
[0]: http://tsung.erlang-projects.org/