Point that sorely needs to be made on Cleave and Great Cleave. I'd take these on most fighters that I want to be able to fight mass hordes, and might even push Great Cleave until after level 10. Here's why.
The commonly-made point on Cleave is that it's useless after level 6 when you get two attacks. Those two attacks are at +6/+1 BAB. In a particular situation, two enemies next to each other (happens fairly often in mass combat or even Xv2 combat), your attacks are then +6/+6 in exchange for a -2 penalty to AC. Great trade in my opinion.
Great Cleave has similar advantages, but against mass amounts of enemies. Imagine you're playing a Level 12 Melee Fighter, with BAB of +12/+7/+2, and you're typically the one in the middle of combat. How often are you going to have three enemies adjacent to each other? Uh, very often if your GM likes mass combat. In this case, your BAB jumps to +12/+12/+12. Yes, only one attack each, but assuming they're weak enough for you to take them out in one hit each, that's a win for you.
My point is that in campaigns where your GM likes to put you in front of multiple monsters at once, or sends high-level PCs against armies, then these feats are situationally much, much better that a high BAB alone, and it's not exactly a rare situation. Don't be afraid to take these for damage-based fighters who constantly get swarmed.
EDIT: As a reminder, diagonal counts as "adjacent".