Paladin's Flames of Devotion ability is a full attack ability, meaning both weapons are used; it also works with ranged weapons. In addition, paladins (both single and multi-class) get an ability that can restore Zeal on kill. In addition, they get boosted defenses (constrained by choosing/avoiding dialogue options that fit/don't fit the order you choose), a (self-)heal ability (presuming you don't choose Shieldbearers), and more.
Rogue might also be another interesting option for several full-attack abilities, as well as mobility and stealth options.
Ranger provides accuracy bonuses, Wounding Shot (IIRC, also a full attack), hit-to-crit conversion if you use the Sharpshooter class, and an ability that, when upgraded, removes 30 seconds from any buff on the target.
I don't know if Barbarian's carnage works with The Long Pain, at least not without the melee-range upgrade. The answer to that question might affect the build's viability for much of the game. Still, Frenzy provides a damage and speed boost, as well as a CON boost. Of course, the first two can be nearly replicated with Swift Strikes and Thunderous Blows.
Chanter might be a slightly counter-intuitive, if interesting choice. Chanter has the Sure-Handed chant, which reduces recovery for ranged weapons, as well as varied invocations that can stun, paralyze, summon, buff, and more.