For performance benchmarking, httperf is at the top of their list. I wouldn't recommend it but only b/c the configuration parameters are very confusing for anything but the most simple tests. For quick gut-checks, I prefer siege (Apache Bench is viable too but it's quirky). For sophisticated or heavy duty tests, I preferred using Grinder or Tsung (JMeter is a time sink). They also recommend Pylot which I haven't used but Corey Goldberg is active on Twitter and other places.

For monitoring they recommend mon.itor.us. They're pretty good but they don't have a free plan. http://browsermob.com/ is pretty cool b/c they use real browsers and they can run your selenium tests.

Some free options for monitoring a single site: http://wasitup.com, http://pingdom.com and http://blamestella.com (that last one is my product and all the plans are currently free).

And remember: what you measure you get!