...a really breakthrough album for its artist. I mean, for example, Michael Jackson's "Thriller" was a blockbuster album and the best-selling of all time. "Sgt. Pepper's" was similar for its cultural impact and huge sales. Could you name an album that was (or wasn't) famous but deserved to be more famous that was it was??

I would say Janet Jackson's "Rhythm Nation 1814". I really think this album is the best pop album ever released. It's stunning. It was a huge success in the U.S., best-selling album of 1990 and spawned 7 Top 5 singles, a record still not broken. But, even so, most of the copies sold were sold in the U.S. And I think RN1814 deserved to be a huge huge huge hit all over the world. Not 15 million copies, it's the kind of album that must sell minimal 30 million.

Off the top of my head, The Isley Brothers' 3 + 3. It was a top ten success when it came out in the early seventies, but it's all but forgotten now. Too bad, really.

http://en.wikipedia.org/wiki/3_%2B_3

anything ever done by squeeze.

modern life is rubbish by blur, but no hard feeligns as its followup made them big

This album is a monster. 'Dreamer' is the worst song on it. Most people say 'Breakfast In America' was their best album, but I disagree wholeheartedly. Every song on this record was a great one and it should have garnished more respect in my opinion.

I always thought  "Al Stewart's Year Of The Cat " (1977) album should have been much bigger and although it was a success in America , it's # 38 position on the UK album chart was a very poor , for such a quality album .
James Blunt sells by the shed load today and neither of his albums match  " Year Of The Cat "

Curtis, by Curtis Mayfield (1970). Superfly, from a couple of years later gets all the credit, but this one- his first without The Impressions, I believe- has several great cuts, "Move On Up" being the best known. Great record; and one of my big faves from the early seventies (Marvin Gaye's What's Going On and Let's Get It On are two others, but they're hardly obscure!)