All IMHO, music is personal taste and not subject to logical argument.
The Grateful Dead are not that great on studio albums. They are awsome live, so to really hear them properly, I would suggest some of the live or Dick's Pick's series. I have a few and about 200 tapes, along with several DVDs. A similar situation applies to Phish.
I also enjoy Progressive Rock such as:
Genesis - Tresspass to Then There Were Three, nothing else (Foxtrot and Selling England by the Pound are the best)
Yes - prior to 90210
Pink Floyd
Jethro Tull
King Crimson
Frank Zappa
Emerson Lake and Palmer
And the better works of the more obscure -
Gentle Giant
National Health
Magma
Banco Del Mutuo Soccorso
Soft Machine
Hatfield and the North
Balleto Di Bronzo
Ozric Tentacles
Thinking Plague
Sleepytime Gorilla Museum
Spoonfed Tribe
Happy the Man
Djam Karet
Area
Semiramis
Tipographica
Arti + Mestieri
Bubu
Brand X
Caravan
DeusEx Machina
Dun
801
Eskaton
Peter Frohmader
PFM
Kenso
Le orme
Egg
Supersister
Van Der Graaf Generator
Yezda Urfa
Anekdoten
... and of course, Anglagard