Anita Baker's debut album also featured Jimmy Haslip on a track (Been So Long), although she was notorious for getting Ricky Lawson, Nathan East, and Greg Phillinganes together and saying, "Make me a hit, boys." That album is definitely in the pantheon.
To me, nothing says "early Marcus" better than Grover Washington Jr.'s 'Winelight' album. Echo on the Luther Vandross stuff, and of course...Jamaica Boys. "You've Got a Friend" never sounded so funky.

Speaking more to Nathan East, along with the names referenced in posts above, I'd include Babyface, Quincy Jones, and of course Fourplay (earlier the better, IMO). There are hundreds, if not thousands, of awesome R&B recordings in this vein. Good luck an enjoy!