Here is a list of hardware, application and platform stress testing applications available in Linux. This list was taken from Ubuntu.
cpuburn – a collection of programs to put heavy load on CPU
crashme– Stress tests operating system stability
ctcs – Hardware testing/burnin suite
ltp – The Linux Test Project test suite
memtest86+ – Scan your RAM for errors
posixtestsuite – POSIX conformance test suite (dummy package)
spew – I/O performance measurement and load generation tool
stress – A tool to impose load on and stress test a computer system (homepage)
stressapptest – stress test application for simulating high load situations
I’ve used memtest86 and stress for the last couple of years to to burn in my server hardware with great success.
Application / platform  testing applications:
fuzz – stress-test programs by giving them random input
hammerhead – stress testing tool for web server and web site
mz – versatile packet creation and network traffic generation tool
siege – HTTP regression testing and benchmarking utility
wbox – HTTP testing tool and configuration-less HTTP server