On the matter of characters behaving with intentions that are somewhat opposite the general "alignment" of an act, my opinion is that a character who behaves in an evil fashion with good intention of mind is evil, and a character who behaves in a good fashion with evil intention of mind is evil.

It's also highly debatable that one of these characters would hold a neutral alignment, however a great abundance of evil caused by NG intentions would likely result in some manner of tainting of the soul, or malicious "branding" of the creature's soul, based on what I've read in the book of vile darkness about great evil acts staining the aura of a place or thing.

An example might be lasting insanity, or gaining foul traits like welts, horns, or an unearthly glow in the eyes.

Examples of how evil acts affect places as per the book of vile darkness might be... ghostly visions and sounds, and the presence of undead and the pooling of negative energy at the site of a place where a terrible God was born, or reborn.

I personally love these concepts of having acts committed affecting the very makeup of someone's negative/positive energy ratio, as undead are supposedly caused in part by a soul being suspended between the material plane and the negative energy plane.

Also true in reverse. I wouldn't be against a particularly adamant Tormish paladin being given the aasimar subrace (and some nice looking golden irises or goat horns) as a result of some overly lawful or celestial-like decision.

This is all mostly food for thought because lots of this could be seen as non-canon, but I think it's good RP and I don't know if the DMs encourage this manner of RP or not.

According to the book o' vile darkness: -Not direct quote, far too lazy to dig through my big box of D&D books for anything but a game, but...-

Evil is not just an action, it is an energy. Negative energy is in us all, and so is evil. To be truly evil, one must embrace evil for evils sake. Anything else is weakness.

At first I wanted to say in D&D morality is consequentialist, while in real life there's always been a big debate whether it's purely your intentions that determine what's good or purely the consequences of your actions. If you cause harm while intending to help, in D&D this is an evil action--exceptions made if you aren't an agent of your actions, like a paladin charmed to slay innocent children. However doing good while intending evil isn't necessarily D&D good, like an evil character consistently aiding his good party because in the end he's planning to take the McGuffin they're all looking for to save the world (or something). It seems that an evil character can only do good by helping without expecting anything in return. So yes I think you're right, in D&D it seems that evil actions are judged by their consequences while good ones by intentions.