One of my favorites!
I'm pretty all over the place --
Classic Prog (Rush, Yes, King Crimson, Zappa, ELO, Moody Blues)
Classic non-prog (Doobie Brothers, Steely Dan, The Doors, more depending on the mood)
Modern prog / metal (Opeth, BtBaM, TesseracT, Plini, Thank You Scientist, Steven...