I know that Arch Enemy and Shadows Fall are pretty big in Japan, ditto Misfits '98, and that Iron Maiden and Cradle of Filth regularly top the charts in the UK and Europe. Germany is one of the most metal-friendly nations in the world (and can you blame them, since they'll forever carry the Nazi stigma, and their economy was in the shitter for the longest amount of time?), and I do believe France has a growing rap fanbase thanks to MC Solaar.
I think the reasons why a band like Arch Enemy is barely a blip stateside and does very well in Japan is partly due to the fact that the Japanese, and I guess Europe, seem to be much more open minded with music and pop culture in general. Things also become much more fad like because of that, but they still have the opportunity to come back.
Stratovarius is a perfect example of this. These guys are very cheesy and poppy sounding power metal. They do extremely well in Europe and Japan...good record sales and financially lucrative touring.
In North America, they barely break the 5,000 mark and wouldn't tour due to lack of people wanting to book them and it not being financially feasible.