For me? The first song I heard was Lateralus on the radio... loved it but didn't catch the name. Then saw Parabola on MuchMusic and loved it... didn't even know that both songs were from the same band.

Bought Lateralus... bought Aenima then Undertow and finally Opiate. I am not picking up 10,000 Days though... not because I think it sucks... not only... but also, cause I'm sick of paying 25-30$ for a CD.