Is there a Mac diagnostics utility for troubleshooting hardware issues? Is there software that helps identify problems, issues, conflicts, etc. with the hardware of a Mac?

I came across Tech Tool Deluxe, which was apparently used in Applecare. Wondering if there was any other hardware diagnostics tool out there.
Looks like Apple Hardware Test is a possible solution. Might need some elbow grease to get it to work on OS X Lion.