Hey, you know those fluffy-wuffy weapons you can set up against charges (they're called spears) for twice the damage on a successful hit? Well, normally, it'd be stupid for you to do that, because it would require you to win initiative, and if you did, then why aren't you attacking? (Not to mention, who'd be stupid enough to charge when they see you're ready for them?)
So why don't you do it like this?
Skewer Counter
People only realize it's a mistake to charge at you when it's too late.
Pre-requisites: Combat Reflexes, Expertise, proficient with spear
Benefit: You can set a spear against a charge as a free action. If someone charges you, you gain an attack of opportunity that deals twice the damage on a hit. You can only benefit from this feat as many times in a round as you have attacks of opportunity. Additionally, on a hit, your opponent's charge is immediately stopped unless he's wielding a weapon with reach.
"Why a free action?" Because you only get an immediate action per round. Also, if you're flat-footed, you can't use an immediate action. A feat that inhibits charging only gets limited mileage as is, imagine if you have to win initiative to use it...
Generally, I say no to feats that allow ranged attacks as reactions, if anything because it's hard to stablish a reasonable trigger for it.
