Hm, cleaving is rather rare so i don't really think that giving a bonus based on a succesfull cleave would be a very good to use as a trigger a special for some special ability, unless that would be a really good one.
As for not counting against a number of cleaves: "great cleave" gives you infinite # of cleaves per round, so i'd just take that one.
Maybe a combination of granting cleave/greatcleave and some other goodie.
My origional plan was to set up a line of "weaker" feats (such as granting cleave/greatcleave) and add some bonus to rage along with it. I'm still looking for appilcable bonusses to rage, but this could be extending the duration of rages/grant extra rage... or something else alltogether. With that, you can pick up some "fighter feats" that only work during rage and improve various apsects of rage along the way.