a lot of people choose warrior in order to use the popular "imbagon" build (check it out at gwpvx.com if you dont know what it is). I find that build to be incredibly boring though.
You could choose elementalist as a secondary prof. for a "conjure" skill, which will up your spear's damage. Similarly, if you wanted to focus on spear damage, you could choose ritualist as a secondary prof, and use splinter weapon for good AoE damage or brutal weapon for good single-target damage. If you use ranger as a secondary prof, you can bring a pet as a supplimental source of damage and utility.
Another strategy is to focus more on support than on damage. In this situation, I would advise using necromancer as a secondary prof. for the powerful curses support skills, and then use these in conjuction with support skills from the command line. You can also use another secondary prof. attribute in a support based build, like smiting prayers (monk secondary) or channeling (ritualist secondary).
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.
You're better off just rolling either a pure Para or a P/W. Yeah there's the boring ol' "Imbagon" but if you're just doing PvE, any secondary is fine. Although, I do occasionally roll a P/Me when I do desert runs.