HEDLEY
Last.fm listener count: 59,482
In terms of appearing-to-be-but-not-actually-being-that-popular, Hedley (fronted by a Canadian Idol third place finalist!!!) are by far the worst offenders. Since the release of their debut album, Hedley's hit singles have been all over the radio in Canada, even though they have almost always failed to chart in the United States (though one of their songs did somehow manage American Top 40 once.)
Hedley's sound can be compared to that of Good Charlotte. At the start of their career, they played whiny, teeny faux-pop-punk, and later in their career switched their sound to even lighter, poppier, and occasionally electro-influenced powerpop. Oh, and they love ballads.
You can catch Hedley headlining over acts such as Our Lady Peace (402,157 listeners) at some piece-of-sh*t music festivals, multiple times a day on mainstream pop radio (but only Canadian radio!), and on whiny teen girls' facebook statuses (I'm not perfect, but I keep trying).
Check 'em out!