Hitachi's Drive Fitness Test (DFT) is very good. It's deceptively simple (pass/fail) but very accurate. It also offers sector repair in select circumstances depending on the outcome of the test.

Memtest86 is great for testing RAM.

I use the two above in addition to Eurosoft's PC Check. I actually like PC Check.

If you want to try something different, I've had some success with PC Doctor in the past. At least I think that's what is was called....been awhile.