Prob Liquid Swords. I was into HH before but that song (and then the album) made me a hardcore fan, but also made me pay more attention to the lyrics, beats, and general imagery they created, everything from the videos, to the design of the cover, the whole atmosphere...made me look out for "complete" art, and it showed me HH is more than capable of reaching the highest forms of art imo. So LS basically led me towards art in general.
Then, Madvillainy. That's the album that I feel really made me want to take my writing "seriously" (not that I've made it my living, but I take more time for it). I still remember when I was listening to it down in Italy in my bedroom and started scribbling away, I think that's when I kind of found my writing style and started feeling somewhat confident about my writing.