I don't think I agree with your second paragraph there. Spells are attacks that you make (using the terminology of making an attack, of which spells are a subset, even though you might more specifically cast a spell), by the quote above (otherwise, casting a fireball or something wouldn't end an invisibility spell). The casting/attack dichotomy doesn't work for that reason, but you have a point. I think you are right in that they aren't necessarily a melee or ranged attack. As I tried to explain in the OP, we need a spell where the attack is part of the spell, not something that goes along with it (as in a spell like storm touch, which energizes your touch for some number of touches), in order for the spell itself to be a melee touch attack. Depending on the exact wording of most touch spells, which I'll have to look up when I get home, this may limit our options severely to entirely.
Also, I did just realize that by the logic of "offensive combat actions", other maneuvers (by the same quote) and full-attack actions qualify, which makes the idea nonsense by reductio ad absurdum. That said, such reasoning doesn't apply to D&D, it just means our conclusion is as stupid as Martial Monks taking Weapon Supremacy at level 1. Also, by this reasoning, I think Arcane Channeling totally works - EDIT: even if it turns out my previous paragraph justifying touch attacks in general doesn't. So we're thoroughly in crazy-town.