Several aspects of a Linux system may need a stress test at some point.

To test the whole system:

stress --cpu 16 --io 16 --vm 16 --hdd 16 --timeout 3600

To test Apache either the Selenium-Plugin for Firefox helps or the Apache bench:

ab -n100 -c100 {url}

Ram can be tested with memtester from http://pyropus.ca/software/memtester/