I don't recall how cleave works in 3E, but since you're experimenting I thought I'd share one of our house rules.One of the things we implemented early on for fighters was this: If you rolled the exact to-hit number, you got a chance at another attack. A specific example would be Sue attacking a kobold. She needs a 9 or higher. If she rolled a 9, than she gets another attack.Using this rule over the course of a year, it adds a bit of excitement. It doesn't come up as often as one might think, but when it comes up it's a small boost in battle morale. Having a plus weapon doesn't increase the chance of this happening.
I was thinking of something related, such as the next unmodified roll must be higher. That gives it a gambling vibe that appeals. It isnalso a function of the characters moving through a low monster HD area of the dungeon. Well give it some more time and see.
I like that it's easy to remember, since the player usually knows the target number they need to hit (Those "barely" hit moments). It's also not guaranteed to do anything and can sometimes lead to a critical miss (if you use those).So the player might get excited and then bam. Similar to when you see fighting on screen and one opponent thinks they have the upper hand and then realizes they don't. ;] Indiana Jones always comes to mind when that happens, heh.That too doesn't happen that often, but it's on everyone's mind when the die rolls on the table.Of course house rules are a dime a dozen and I'm sure you guys will come up with something.
You could do it this way: every time a Fighter fells a bad guy, he can attack an adjacent bad guy.Works really well against peons, but isn't totally useless against high-level monsters either.Alternately, you could use the old Chainmail/OD&D rule where Fighters get to divide their level by their enemies' level to figure out how many attacks per round they get.So a 4th level Fighter fighting 1 HD monsters gets 4 attacks per round. Fighting 2HD is 2 attacks, and anything else is 1.