Favorite artist/band of each decade?
 

Here's my list:

50s: Chuck Berry
60s: The Beatles
70s: The Who
80s: Bruce Springsteen
90s: Blur
00s: The White Stripes

are we going by when bands formed or when they were active?

In terms of who were the best act each decade(not when they were formed), I'd go with...

50's - Elvis
60's - Beatles
70's - My head tells me Led Zeppelin but hey, I'll be honest! I'm going with the calming influence of the Eagles!
80's - Bruce Springsteen
90's - R.E.M.
00's - Bell X1

50's- Chuck Berry
60's- Bob Dylan
70's- Sex Pistols
80's- Echo & The Bunnymen
90's- XTC

I haven't heard enough modern music to really give a favorite artist for the 00's.

50's: Hmm...Mingus
60's: Simon & Garfunkel
70's: King Crimson
80's: Tom Waits
90's: Public Enemy
00's: Spoon

50s: Thelonious Monk
60s: The Beatles
70s: King Crimson
80s: The Smiths
90s: RHCP
00s: Isis

50s: Howlin' Wolf
60s: Bob Dylan
70s: Brian Eno or Elvis Costello
80s: Pixies or Dinosaur Jr. and maybe Rites of Spring, and Fugazi if they count. 80s is a hard one for me.
90s: Modest Mouse
00s: Against Me!

50s: Miles Davis
60s: Beatles
70s: King Crimson/Pink Floyd
80s: Metallica
90s: Burzum
00s: Pain Of Salvation

Some of my favorites like Rush, Testament, Opeth & Radiohead couldn't be placed in any particular decade.

50s:none
60s:Pink Floyd (Barrett lead era)
70s:Joy Division
80s:Sonic Youth
90s:Blur
00s:Radiohead

50's: Johnny Cash
60's: Oh i don't bloody know. Jimi Hendrix Experience. Maybe.
70's: David Bowie
80's: The Smiths
90's: PJ Harvey
00's: Too early to say! At the mo, The White Stripes.