(Evo - feel free to merge this if you see fit)
I've used SiSoft Sandra and Belarc Advisor before to analyse systems I have been working with, but came across
PC Wizard this week which blows the others away IMHO.
Freeware, it tells you absolutly everything you could possibly want to know about what is inside (and running) on your PC.
The homepage has some other programs you could try (CPUID is well respected). Find it
here.