Warrior, obviously (shouts, better IaS). It's pretty much the only secondary for Paragon.
There is some applications for Monk (better Prots, hex removal), Ritualist (better IaS, various weapon spells), Necromancer (enchant removal, more battery skills), Mesmer (enchant removal, hex removal, interrupts), Elementalist (conjures, more burning, blind) and Ranger (Poison, better self-condition removal) too though, as far as more generalist Paragon builds are concerned.
Assassin secondary can work too, if running a gimmick build.
Vast majority of the time you'll be sticking with mostly Paragon skills though, with an odd Warrior shout or two, or an elite from another profession (because most of the Paragon ones suck), thrown in.