For basic load-testing Httperf and Apache Benchmark are nice. If you want more complicated stuff (really simulating a user taking actions on your site) I'd reco

For basic load-testing Httperf and Apache Benchmark are nice. If you want more complicated stuff (really simulating a user taking actions on your site) I'd recommend leveraging Selenium or even plain PhantomJS (setup a separate server to spawn those processes and hit your main site). And yes, it will stress whatever site you're testing. In most cases, you'll want to setup another site (make it an exact replica of your main site) and direct your load tests to hit that alternate site instead.