your favorite 3 Duke Ellington albums?

I'd add Money Jungle with Mingus and Roach. Wild and hard-hitting.

I'm not a big jazz fan, but enjoy the earlier Ellington stuff. Specifically these 2 cd's:

Swing Legends - 24 Classic Hits, Robert Parker series. 1920's to 1940.

Sophisticated Lady, Victor Jazz, 1940-46.

Both have excellent sound for the time period.

Ella at Duke's Place
Blues in Orbit
Never No Lament: The Blanton-Webster Band

It's not "technically" Duke... but since you already like "Side by Side", you should hear "Johnny Hodges with Billy Strayhorn's Orchestra.  It's one of my all-time favorites regardless of genre.  I see where it is available on a 2013 SACD release.  That should really be special!

Johnny Hodges and Strayhorn also one of my favorites.
If you haven't heard the Hodges recording "Everybody Knows", you
may want to check it out.  Same genre.  The orchestra, these
guys were pros, all on the same wavelength.  Simply wonderful music.