Well... really that would be Post-post-WW2 guns and such in terms of weapons for the 'era'. However, since firebending in metal pipes replaced cannons... well, we have to come up with something better than the zappy glove, don't we? 

Mecha suits aren't really my thing, since a few episodes in to LoK, Asami's father, a villain, is in one, plus they're rather bulky. (I've watched some of it, a while back.) And proper pistols aren't really something that a good guy would use, since we won't really be looking to kill people as Team Avatar, right?

One idea I had was a sort-of samurai/ninja person in the modern age - so they've adapted bending styles into physical hand-to-hand, seeing that that's what bending is in the end. Whether or not this style could be augmented with weapons is something else, though.

Just a thought.