You gotta get some of the second great Miles Davis Quintet - possibly the most worshipped group of musicians in all of jazz - Miles, Wayne, Tony, Herbie and Ron. Circle remains the most beautiful Miles ballad.
Sun Ra's catalogue is so immense that it can be very intimidating. This is a perfect place to start (just make sure you have lots of disposable income cos Sun Ra fans always turn into avid collecters!). Not to out there, but definitely different. Awesome space jazz, exotic landscapes, tribal drumming, big band jazz. Nifty.
Duke Ellington's discograpy is almost as big as Sun Ra's. This is a perfect staring place, this one properly clicked me on to Ellington and I since became a rabid fan. More of a laid back good times session this one
Just buy it! 4 disc set of exceptionally inspired Coltrane with Elvin, McCoy and mr Eric Dolphy!