I'll have to list quite a lot to cover everything... this isn't in any real order:
Dream Theater's "The Glass Prison" got me out of nu metal and into progressive metal in general.
Yes' "Close to the Edge" showed me that prog needn't be metal to be awesome.
Aqua's "Roses are Red" showed me how awesome dance electronic music is, and confirmed to me that I needed to include electronic elements in any music I create.
Lady Gaga's "Bad Romance" cemented that.
No Doubt's "Tragic Kingdom"... the entire album, really... got me into female driven rock.
Bat for Lashes' "Daniel" got me into more "indie-ish" female driven pop/rock.
Tegan and Sara's "The Con" firmly cemented that.
Arch Enemy's "Nemesis" got me used to growled vocals.
Dimmu Borgir's "Progenies of the Great Apocalypse" showed me the potential of black metal in general.
Nightwish's "The Pharaoh Sails to Orion" got me into symphonic metal in general.
Epica's "Consign to Oblivion"... the entire album... again cemented that.
Eternal Tears of Sorrow's "Tears of Autumn Rain" showed me how beautiful heavy metal can be, and how large an effect lyrics can have on my perception of the music.
Devin Townsend's "Bend it like Bender" showed me how mixing and defying genre altogether is the best way to think about music.
Opeth's recent release "Heritage", a total work of genius, did a great job of confirming that.
Dream Theater's "The Glass Prison" got me out of nu metal and into progressive metal in general.
Yes' "Close to the Edge" showed me that prog needn't be metal to be awesome.
Aqua's "Roses are Red" showed me how awesome dance electronic music is, and confirmed to me that I needed to include electronic elements in any music I create.
Lady Gaga's "Bad Romance" cemented that.
No Doubt's "Tragic Kingdom"... the entire album, really... got me into female driven rock.
Bat for Lashes' "Daniel" got me into more "indie-ish" female driven pop/rock.
Tegan and Sara's "The Con" firmly cemented that.
Arch Enemy's "Nemesis" got me used to growled vocals.
Dimmu Borgir's "Progenies of the Great Apocalypse" showed me the potential of black metal in general.
Nightwish's "The Pharaoh Sails to Orion" got me into symphonic metal in general.
Epica's "Consign to Oblivion"... the entire album... again cemented that.
Eternal Tears of Sorrow's "Tears of Autumn Rain" showed me how beautiful heavy metal can be, and how large an effect lyrics can have on my perception of the music.
Devin Townsend's "Bend it like Bender" showed me how mixing and defying genre altogether is the best way to think about music.
Opeth's recent release "Heritage", a total work of genius, did a great job of confirming that.