I personally like the Blockhead (Always Incendiary. Fires a unique 3x3 spread of fireball blocks that ricochet off of surfaces.) and the Heart Breaker (Always Incendiary. Increased projectile count, fire rate, and critical hit damage. Shoots in heart shaped pattern. Any inflicted damage returns health to the wielder (2% of damage).)
Hellfire is great since it gets 50% bonus splash damage like a plasma caster and only consumes one ammo.
The Blockhead is awesome for the same reason, as well as having a good projectile count and consistent accuracy.
The Volcano, despite what the above poster said, actually outdamages a Snider. It has lower damage on the damage card, but it does an additional 80% splash damage compared to the 50% of the Snider. A Pimpernel is, of course, great, probably the best sniper rifle in the game period, or close to.
The Longbow is damn powerful, but a bit tricky to use at range.
The Seraphim is now pretty damn good after its buff, preferably with the Deep prefix to compensate for its projectile speed.
Greed is a fantastic pistol because it gets the awesome Jakobs critical damage and good movement speed while sighted.
Just about any awesome legendary that is great on its own and is available in incendiary will be great, like the Conference Call or Lyuda.
Heart Breaker is pretty good and heals.
Good Touch is good in lieu of a Hellfire.
Plasma Casters and Blasters work great, same with Slow Hand.
For grenades, the Fire Bee is pretty ridiculous, though any Fire Burst will be damn effective as well.