Repulator is a very simple AddOn that adds some perks to the Reputation Frame that makes at-a-glance understanding a bit easier. The AddOn does two main things:
Modifies rep mouseover to show remaining balance needed
Colors (adds abbreviations in WotLK) rep name based on standing
There's no configuration, just drop and go! Doesn't do anything crazy, doesn't redesign your entire Reputation frame. Avoid getting the calculator out to figure out how much Rep you need to the next standing!