Another tool is MZBench. It takes a different approach to tsung in that it is request rather than user session oriented. It is also a bit more approachable in its web UI, and writing load tests is rather more straight-forward. It does not have all the functionality (by far!) of tsung, but if you just want simple request load testing, it’s pretty good. It also supports clustering and cloud hosting out of the box with rather simple setup.
I now use both, depending on what I am trying to measure.