Scouts and Mounted Combat-

[StreamOfTheSky]

As I recall there's a feat that allows a character with Sneak Attack, Sudden Strike, or Skirmish to do half of the normal damage of that ability against foes immune to critical hits. I know for sure it's in one of the splatbooks.

Not a feat, it's Penetrating Strike from Dungeonscape. Replaces Trap Sense. Melee only, unfortunately. Death's Ruin in C.Champion is similar, except not melee only, but only applies to undead, so it's worse overall.