Can't pick a favorite. If pressed, I'd probably list my top three as:

Pink Floyd
Jethro Tull
Rush

Heavy metal: Judas Priest, Uriah Heep
Doom metal: Candlemass, Trouble
Thrash metal: Overkill, Nuclear Assault
Speed metal: Metal Church, Megadeth
Black metal: Mercyful Fate, Bathory
Death metal: Death, Bolt Thrower
Prog metal: Fates Warning, Psychotic Waltz
Power metal: Virgin Steele,
Prog rock: ELP, Wishbone Ash
Electronic: Tangerine Dream
add King Diamond somewhere.

Genres given just to point out i don't have a "one fav" band. It was hard to point one in a genre, especially that they're 'fluid'.

Number one? Nick Cave and the Bad Seeds. Never get tired of them. I'm also very fond of the Beatles, so they'd probably make it to number two. Followed by all sorts of other stuff. My collection is very eclectic.

Pink Floyd, although Gary Moore comes very close in the "artist" category.

Sabaton. Military history and metal have always been a couple of my biggest interests so it comes as no surprise that my favorite band combines them.

Soooo many bands / artists that I really like, hard to nail it down to just one. It's probably a 3-way tie between Rush, Scorpions, Neil Young, Tesla, The Bodeans, Kevn Kinney, and a couple dozen other bands. ; )

This.

And also:
Metalcore: Silent Civilian
Rock: Journey
Cello rock: Apocalyptica
Symphonic Metal: Within Temptation

If I had to pick one, probably Opeth.

Depeche Mode who I listen to 90% of the time when I play music

Other groups/artists of interest:Faithless, The Prodigy(older stuff) Beastie Boys, Rob Zombie NWA(and all its individials work),DMX, INXS I like the synthpop groups quite a lot

Basically anything not originating in the last 5 or so years as it seems music really took a nosedive

Flaming Lips, Pixies or My Bloody Valentine instantly spring to mind but I'd also rank Slowdive, Pavement and Yeah Yeah Yeahs (for Fever to Tell alone) among my favourites.

Has to be Amon Amarth or Ensiferum :>.

EDIT.
Also enjoy some unknown tsugaru shamisen group.

Alice Cooper, Sentenced ... and Body Count ! Good Ol' Bands, eh ?

... I tried to make a top three but I have to give credit to Iron Maiden, Slash in general, Clapton and sooo many others ... but these are the main ones.

Only one?

Above & Beyond, I guess.

It's long been a tie for me between Tool and Rage Against the Machine. I don't bother deciding between the two as they both represent what I see as two different sides of myself (emotional/spiritual and political/personal).

A couple tunes for first timers:

http://www.youtube.com/watch?v=07pLGIgyfjw

http://www.youtube.com/watch?v=rASyDOCSmb0

I'm not sure there's another band with more intensity on stage than RATM.