Martial Power 2 introduced the Shinaelestran Guardian paragon path for Rangers.
One of its features is the Guardian Defense.
Guardian Defense (11th level): Whenever you gain a bonus to attack rolls from one of your ranger class features, you gain a +2 bonus to AC until the end of your next turn.
I think the intent of this feature is to work in synergy with either Prime Shot (from Player's Handbook) or Running Attack (from Martial Power 2).
If none of your allies are nearer to your target than you are, you receive a +1 bonus to ranged attack rolls against that target. You do not gain this feature if you choose the Beast Mastery fighting style.
This class feature replaces the Prime Shot class feature.
If you use a standard action that lets you move (such as a charge or the skirmish shot power), and you end that movement at least 2 squares away from where you began that move, you gain a +1 bonus to attack rolls made as part of that standard action.
These feature are very situational and thus the Guardina Defense's AC bonus doesn't kick in all the time. However, Heroes of the Forgotten Kingdoms later introduced the Hunter and Scout implementations of the Ranger class.
Hunter's Weapon Talent and Scout's Two-Weapon Style (Flashing Blade Mastery) both grant a +1 bonus to attack rolls with every attack.
You gain a +1 bonus to the attack rolls of weapon attacks.
TWO-WEAPON STYLE Gain flashing blade mastery or spinning axe mastery.
Flashing Blade Mastery
You gain a +1 bonus to weapon attack rolls while you wield a light blade in your off hand.
Spinning Axe Mastery
You gain a +2 bonus to weapon damage rolls while you wield an axe in your off hand.
By RAW it seems that every weapon attack will trigger the +2 AC bonus. However, it seems questionable because of the specified paragon path came out before these classes have been published, and it seems like an unintended synergy.
Is there any official FAQ on the matter?