Which century? In the 24th, we've got Picard/Crusher, Riker/Troi, and Paris/Torres. In the 23rd, there's Robert and Sarah April, but I can't recall if the books that use them depict them as being married while they served together.
Also Geordi's parents ... though, again, 24th century. And the Crushers would presumably have been a Starfleet couple if Jack had lived.
As far as the 23rd-century Novelverse goes, the Lost Years books show failed or failing marriages between Kirk and Vice Admiral Lori Ciana, and Kevin Riley and a security officer named Anab Saed.