Iron Maiden
Megadeth
Rush (well, until this latest album)
Deep Purple (as long as Gillan is singing, although Coverdale wasn't too bad)
Roth-era Van Halen
These are my all-time favorites here. As much as I like bands like Borknagar, Meshuggah and Opeth, these bands have been in my favor for over a decade each. Honorable mention goes to:
Black Sabbath
Led Zeppelin
Opeth
Borknagar
Ritchie Blackmore's Rainbow
UFO
the Police
King Crimson
Focus
Jethro Tull
Pink Floyd
Anthrax
Testament
My lists always end up too long...I'll end it here because I could go on until I have every band in my collection named. Needless to say, in comparison to the rest of the lists here, it's as if I were a million years old.