Though several DMs have done so in the past in games I've played in, I'm not exactly a fan of rewarding players for "role-playing" (as it is often mistakenly identified), but for role-playing of any type. I also like players who actually create a character history, especially if it gives me tender bits to chew on when writing adventures. It was mostly a problem of determining a viable reward that they would actually give a fuck about but doesnt mess with long-term balance.
See, extra XP in 4E isnt terribly useful since you no longer have to burn it in order to make magic items, and it would take quite awhile for it to accrue to the point where you are leveled temporarily higher than everyone else...assuming no one else is also hoarding bonus XP.
So, no, thats out. Some ideas that are in are as follows.
- A bonus action point that never "decays", and can be used in the same encounter as another one.
- Add +1d6, +1d8, or whatever to an attack roll or skill usage.
- Recharge a spent encounter power.
- Recharge a spent daily power.
- Remove a spent magic item power usage.
- Act as if you got a 20+ on a death save.
- Typed bonus to attack rolls, damage rolls, defenses, etc.
- Untyped bonus to attack rolls, damage rolls, defenses, etc.
- Automatic critical hit if an attack hits at all.
For example, if a friend or loved one is being attack by a monster, I might grant a bonus on the attack and/or damage roll. If a player is on their last leg trying to defend someone or thing, I might give them a power bonus to defenses to represent their determination. A chaos sorcerer might get a variable bonus to an attack roll. Think any scene in any media where an adrenaline rush of sorts pushes the character to do something particularly badass, or just pick an anime where rage-bullshit kicks in to save the day.