Wish this forum had a "polling" feature, it might be helpful in getting some great music re-mastered properly and re-issued.
My nominees. Iron Butterfly's In-a-godda-di-vida (long version). Sure it's a stoners dream but whoever mixed this mess should have been sober when they mixed it. It has one of the best drum solo's ever recorded in Rock and it's a damn good "song" overall. Unfortunately, whoever mixed it had a lot of high frequency hearing loss and the "ping pong" channel mixing was out of date about a week after it was first tried. I know that the tape hiss really can't be fixed but, please, would Mobile Fidelity or someone similar get the master tapes and do something about mastering it properly?
Credence Clearwater Revival. ALL of the Fantasy re-issues. Great music totally DESTROYED by a completely DEAF idiot at the console. These are the only LP's that I own that I would consider totally unlistenable. Which is a crying shame because CCR produced some really great and interesting music that I didn't "get into" until after the original LP's were long gone.
That's my 2 nomineees and I am quite sure that there are lots more out there, lets hear them.