. . . and perfect timing. One of my Christmas presents was a 3-CD deal with songs of the 60s. Listening to them now - some of them are soooooooo awful I can't believe that we thought they were great at the time. But some of them have certainly will passed the test of time.
CS&N is certainly on my list - but I would add perhaps Janis Joplin, Spirit, and who could forget Black Sabbath? I think that Moody Blues have been brought forward with the instrumentalizations in many pieces today.
I would like to think that Jefferson Airplane, (Jefferson Starship, Starship), has had some influence, along with Fleetwood Mac. Gee, how about Creme?
All these great old groups just keep popping up in my mind - and I almost for Carlos Santana - he has so much of an influence that he, thank goodness, is still with us. He has been a HUGE influence and no list for your question should be without him.
Wow! What a trip down memory lane you just gave me! Thanks for reminding me of the many concerts at Fillmore West, Winterland, the first Days on the Green in the SF Bay area, and many many other concerts that I attended (usually for less than $10/concert. Those were the days).