List of artists that have never lost quality throughout entire career


One of the brightest on my list is 

1. Depeche Mode. I'm big fan started listening and enjoying them from their very first album "Speak and Spell". I am devoted to their perfection of every song they create in terms of sound, melody, harmony and incredible intelligence. Their music may seem simple, but in reality much more complex than seems. I believe that they're somewhat commercialized, but also believe that they deserve their incredible success. They're indeed Kings of electronic rock!

2. Can (The Can). Every album they released is a journey to their creativity. What are they rock? Jazz? Prog? Their music often can cover all styles of music in one song. It's a blend of jazz-trained drummer Jaki Libezeit, classically trained keyboardist Irmin Schmidt(also conductor and neo-classical composer and film score composer), multi-instrumentalist bassist Holger Czukai and classically trained guitarist and electric violinist Michael Caroli (RIP). It's a unique blend of musicians with extraordinary skills and creativity

3. Dead Can Dance. This artist has plenty of praises and each and every of their album is a unique blend of electronics and earth bound instruments. Lisa Gerrard is known to be a part of Gladiator Motion Picture Soundtrack.

4. Tom Waits. Many would criticize Tom for not singing his own voice, but I'm amused the way he does it with spirit of Louis Armstrong! Yes indeed with spirit instead of just imitating. Embracing the spirit of inspired artist is different and Tom is clear example to that!
czarivey
Agree about Springsteen. Also my personal favorites: Paul Simon and, especially, Leonard Cohen. Cohen's last concerts were masterful and kept getting better.
I can't say I've really followed an artists whole career except for the Grateful Dead.  But, here are a few that as of now have not let me down. 
Zappa
Neko Case
Dan Hicks
Brand X
Gentle Giant

I almost forgot Jimi, start to finish. Of any artist I can think of his was a star I can not help to feel saddened by the what if's
Steely Dan, Frank Zappa, Bob Dylan, Oscar Peterson, Dizzy Gillespie, Ry Cooder, Dire Straits, Mark Knopfler, Willie Nelson, Beatles, Miles Davis, Led Zeppelin, Talking Heads, Frank Sanatra, Joni Mitchell, K.D. Lang, CCR, There are many more but this just came off top of my head.

Some really big names, some my favorites I've left off because the have a few so, so or not so good albums.