To me, Sigur Ros has made the most beautiful music of all time. ;D I love them!
Their sound is always epic, with piano and violin masterpieces subtly mixed with post-modern sounds, but with many variations across their albums.
Their first album, "Von", is a bit varied, but a great example would be its namesake, "Von": http://www.youtube.com/watch?v=F6LCbJe1dmg
Their second album, "Agaetis Byrjun", is the quintessential Sigur Ros, having many fantastic songs like Staralfur (probably my favorite), Agaetis Byrjun, Svefn-g-englar, and Olsen Olsen: http://www.youtube.com/watch?v=j2GjOC79gVI
Their third album, "()" (aka Untitled) is a departure from their other work, with themes derived from the beautiful and sad piano song "Untitled #1". The music video is particularly touching and even foreboding: http://www.youtube.com/watch?v=hqJ8hFgYwVg
Their fourth album, "Takk...", goes back to basics, with epic songs like Hoppipolla: http://www.youtube.com/watch?v=hnAwPeqrdAk
Their most recent album, "Með suð í eyrum við spilum endalaust" is overall very playful and upbeat, with festive songs like "Inní Mér Syngur Vitleysingur": http://www.youtube.com/watch?v=HiOU9NAiYlQ
As you have said, Jonsi's solo album is also excellent and carries the spirit of the band very well. I recommend his album too!
Sigur Ros is definitely an underrated band, with a beautiful sound unlike anything else in music today. I wish more people tuned in to their music, they would feel nice and even thankful for knowing such beauty! (IMHO
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