I stumbled across the '75 studio sessions last night on the archive. If you haven't heard these they're really worth listening to. Of special interest to me was on 3-17-75, where keyboardist Ned Lagin and David Crosby hung out with Phil, Jerry, and Kreutzmann and just messed around and jammed all day. There's a transcript of a radio interview somewhere out there with Ned Lagin talking about that day. From all the giggling and diologue in the background I can only assume they were all tripping, lol. There's a lot of really cool jams, including some based on the theme of Crosby's tune "Low Down Payment" but there's one track in particular that sticks out, a 25:00 or so jam that starts out very spacy but ends up turning into a lot of rhythmic and harmonic interesting-ness by 10-12 minutes in. Very cool. Sound quality is pretty great, too. Check it out!
Those are some of my favorites to listen to. I've had access to the many 75' sessions for a while and they are always getting a spin. Both Sugarmegs and Live Music Archive have all of them if you haven't had the chance to hear the rest. But yeah, that session with Crosby and Lagin is a trip to listen to.
http://www.archive.org/search.php?query ... %221975%22