Any good PC diagnostics freeware?

I'm curious if anyone knows of any good, free PC diagnostics software. I'm looking for something that offers PC diagnostics, S.M.A.R.T. technology to test hard drives, checks for errors, and provides system monitors and a system explorer type function....to make sure that everything is in fine working order (and not about to crash!).

Does such an animal exist? Does anybody know of a good program to check this sort of stuff out?

 

I'm not sure if these exactly fit the bill but there is EmsaFlexinfo and Emsa DiskCheck from http://www.e-systems.ro/flexinfo.htm

Also HDTune from http://www.hdtune.com/

At least that will get you started. (I use the above on XP Home without problems.)

 

There may be others but SiSoft Sandra is pretty comprehensive.

 

Another one: EVEREST

 

Thanks, guys....these are all pretty good ones. And bch.....thanks for the two freebies, those are exactly what I'm looking for....

 

Seagate has it's own diagnostic software for DL
http://www.seagate.com/support/seatools/
I'd assume other HDD manufacturers would have similar...