TinyDPS or Skada should do what you're looking for, I think both eat a little less memory than Recount. That said, I've never experienced an issue with Recount myself.
And what Lulia said about exiting combat is pretty much spot on. Exiting combat is not based upon time, it's based on either being the last one still alive or, when running, the distance traveled since your last active hostile action towards the mob (which includes getting inside its aggro range).