The Infamous Scamola said:
Anything by Black Sabbath, Ozzy Osbourne, Metallica, Judas Priest, Iron Maiden or Motorhead.
Can't go wrong with the classics.
I'd have to say I'd take NWOBHM bands over Slayer, Slipknot, or SOAD any day of the week. In short, most modern bands which function on "xtreem bass riff, d00d", guitar mush, and over-the-top show efforts are trying too hard. Of course, because there's a bit of stylistic difference there, fans of the latter draw distinctions between metal and heavy metal as two different things. Classic hard rock and heavy metal are my preferred poison.