Are there any sites with good boss AI and ability descriptions?

[Lissa]

I do not know of any site like this, but specifically about Rakanoth, if you are not within 10 yards within a couple seconds (even if Rakanoth teleports), he performs an instagib move that the only way out of it is either get lucky and dodge it or have some kind of power that forces him to target something else (smokescreen -- works, mirror image -- need confirmation from a wizard that has used it, not sure on WD). Rakanoth is deadly to ranged classes because of this instagib move he does (and no matter how much health you have or how much armor you have, you die if hit).

His attack is not insta-kill at least on hell and below. It took him hitting me three times that way during one potion cooldown to kill me. I had about 40k life, 5k armor, and decent resists for Act 4 hell at the time. I can take a hit on occation, but I need to discourage him from doing that to me too many times in rapid succession, which is why I need to understand his AI better.

Well, for a DH with 33k health and 4k armor in hell, it's an Instagib cause DH does not have a reliable damage reduction skill.