Lwaxana Troi in a few episodes of DS9.
Will Riker in Voyager - Death Wish.
(Tom Riker in DS9 - Defiant.)
Q in DS9 - Q-Less and several Voyager episodes.
Picard in the DS9 pilot.
Barclay and Troi in several Voyager episodes.
Riker and Troi in that horrible Enterprise finale.
Worf and O'Brien in quite a few DS9 episodes, obviously.
Admiral Nechayev appeared in DS9 as well.
Gul Evek appeared only once in TNG I think, but he was in several DS9 episodes and the Voyager pilot.
Spock and Sarek each appeared in two TNG episodes, so you might call them recurring. They appeared in TOS of course.