Spirit was one of my faves back in the day. The stuff still sounds fresh. We play "Line on You" in my band, perhaps not Spirit's best effort but a crowd favorite. "Fresh Garbage" actually got radio play back then even though it was not released as a single. Can you imagine anything like that getting airplay today?
Another favorite from back then was Colosseum, kind of a jazz-blues-rock fusion thing. But I don't think they made an impression in the States, and never had a "hit" so don't qualify for the spirit of this thread.
Here's a great band that DID have Top 40 hits, though:
When was the last time an actual band was featured on a televised award show, as opposed to some stripper with elaborate dance numbers and a prerecorded backing track?