Just what the question states. Normally, I only want to know if there are any nodes/passives that boost Chaos Damage, and whether or not it is improved by Spell Damage nodes, but might as well make it a broad question.
So far, the wiki doesn't list any passive to improve Chaos damage type (while there are options for physical and elemental damage). There's only a line about a notable passive, but it doesn't really increase chaos damage:
There's also a conversation in the official forums entitled "Increasing Poison (Chaos) Damage?", but to be short, there are no passives mentioned: the best way remains to level up the gem.
In another chaos damage conversation, I've found this answer (given on September 7, 2012):