DrJ - I'm a big Moby Grape fan. Been one for many YEARS!
I'd suggest checking out their first album. I really think it's a perfect record.
Basically, you had four vocalists, three guitars, groovin' bass. They had talent to spare.
On the guitar front, you had Skip Spence playing rhythm (in his own cool style), you had Peter Lewis fingerpickin' and you had Jerry Miller playing great lead.
On the vocal side, you have great harmonies on every song, plus most members took turns on lead vocals. My favorite vocalist being Bob Mosley (who was the bassist) who had a huge vocal range and sang quite soulfully.
Ghost mentioned Skip Spence. He is one of those casualties of rock (like Syd Barrett). The story is, during the sessions for their second album in New York, Skippy was dating a witch and taking too much acid. I guess the combo didn't serve him well and he attacked another band member with a fire ax.
He was arrested and spent six months in Bellvue. Upon his release, he drove a motorcycle to Nashville and recorded the album Oar in a few days, playing all the instruments himself. He never really recorded much after that. A couple years later he appeared on a Moby Grape reunion album, but he wasn't nearly as present as he had been on their first album.
I'd highly recommend the first Moby Grape album and Spence's Oar. There was a Moby Grape compilation called Vintage put out by Sony around 10 years ago. If you see a used copy, I'd grab it.