Do you know of any hard rock or heavy metal albums with pop appeal? I remember "Back in Black" by AC/DC, but I've read that Def Leppard's "Hysteria" also crossed over to the pop market. How about the Deep Purple albums? I've only got "In Rock", but I think that might also fit the bill.

IMO the whole 80s Hair Metal would fall into that category...

Def Leppards previous release "Pyromania" also crossed over, with high charting singles. I agree with the above, all the 80s hair bands, Poison, Winger, etc, etc. Not my kind of music at all, but definitely huge crossover appeal.

As a more modern example, Nickelback seems to have achieved a similar feat...

Metallica's black album.

That was my first thought, too.

I think Def Leppard's "Hysteria" is the definitive hard rock/pop crossover album, with Bon Jovi's "Slippery When Wet" a very close second.

Arrowsmith's Permanent Vacation, Pump and Get a Grip were all pretty pop-oriented.

Deep Purple - Machine Head