I saw them in Central Park, NYC, for free, once. It was around the time that the album Volunteers came out.

I used to have the single of Mexico/Have You Seen the Saucers? (sleeve pictured below), released in 1970. It was one of the first 45 RPM's in stereo that I ever owned.

I haven't heard it in years, but their first live album, Bless It's Pointed Little Head, is GREAT whether you're stoned or not. Jack Casady's bass playing is the best thing about that band, and he really stands out on this record. I never heard it on CD, only vinyl.