Yngwie is into Bach's litte brother or something. Love yngwie (Sweet spasmoid vibrato), but...
Legit wise, Bartok, Bartok, Bartok. Makes Spiral Architect look repetetive.
If you slay guitar, please make villa-lobos Etude #11 a metal tune (mmm...octaves).
Brower studies (Diary of a Madman is note for note, then extrpolate) are worth a pilfer.
Yellow shark (Zappa) befuddled a really good string quartet.
For quartal and quintal chords (stacked 4th's or 5th's), DeBussy. Be forwarned, smurf-level happiness.
Other than that, where's the backbeat???