A casual disarm mechanism is to aime for the arms of your opponents. So a critical attack, with ranged or unarmed/melee can cripple your enemies bodypart and so disarm him.
In melee, the perk "in your face!" sounds nice, but i read that its broken right now. Otherwise, it would be a nice perk for every melee fighter.
I'm missing good melee perks too. With the trait heavy handed and a mega powerfist, you can keep your opponents almost down, but the melee dmg is not that high. A super sledge give you more dmg, but hits your enemy out of your range, not that cool. Some kind of "sword" (like the ripper, but even bigger) with a penetration perk or so would be nice. The super caddle prod, for example, got the accuracy weapon perk, which is not that usefull...