Today is just a quickie but one rule I adapted from a friend of mine is the "player deathblow" rule.
This is simply a narrative device but whenever the party is fighting something big and mean, when the death blow lands turn the table over to the owner of the character that did the final hit.
That player get's to describe in full glory exactly how he or she dispatches the fiend.
No rules advantage, no extra mechanics, just a moment to shine after a tough fight and a way to help encourage a little extra roleplaying in a campaign.
Do you use any similar narrative devices in your games?