BurnIn Test is a pretty stressful test for the system.
runs (user config.able) 8-10 tests at once. 8-10 spawned windows everything from reading and writing to every single disk /logical partition on disk, optical drives, drawing 2d, drawing 3d, alu and fpu ops, mmx/sse/multimedia ops etc. for cpu, network test, com port tests, memory tests of reads, writes and verificaiton of simple to complex bit patterns. it might not therefore stress the disk or other parts to it's fullest capacity b/c of so many parallel operations but it's a great system tester, atleast was for me!
all in all, while synthetic benchmark, it's specifically ment to test the stability of your system. looks like it's shareware and runs max of 15 strainht minutes, but believe me, you will find a lot of problems well before that if you do have them.
of course, as mentioned before: prime95's torture test, seti, sandra's few cpu/mem/drives benchmarks are good as well.