Combat Prowess
Essentially, Combat Prowess is a pool of points that may be spent to modify attacks in various ways. The options available are limited by level, as is the number of times they may be used in a given turn. The options are:

Most of them are pretty self-explanatory. It is worth noting that any points used apply to only one attack in a given round. That is not to say that points may not be spent on more than one attack, however. So, if you spend 1 point for an additional attack, giving you 2 attacks, you may spend one point on each attack for a +1 to-hit on each. In this case, you would be using a total Prowess of 3 points.
Effect C, -1 enemy "to hit", applies to a single enemy, but it does apply to all attacks from that enemy.
Effect D, +1 to critical range, improves the critical range. +1 improves the critical range to 19-20, etc. A critical hit will be indicated by any natural roll within the range.
Effect E, Additional attack, grants the combatant an additional attack. Additional attacks are not modified by Prowess unless points are allocated specifically for them.
Effect F, +1d6 on a critical hit, allows an additional d6 to be rolled and added to the damage total in the event of a critical hit. Note that Prowess must be allocated for this effect before the attack is rolled, so it is a bit of a gamble, though the bet may be hedged by also allocating Prowess to Effect D.
Effect G, +1 Initiative, is added as a general bonus in group initiatives. That is, all bonuses from all characters are added together, then divided by the number of characters to arrive at an average Initiative bonus. Of course, in an Individual Initiative situation, it is added directly and unmodified.
Prowess is gained differently for each class. The following table illustrates when each class gains points, which effects they are eligible to employ, and how many points may be allocated to a given effect each turn.
* The number of times a letter appears indicates the number of points that may be allocated to that effect in a given turn. For example, a 7th level fighter has 4 Prowess points, and access to effects B, C, and E. In any given turn he may spend 2 points on A, 4 points on B, 2 points on C, 2 points on D, or any combination not exceeding the total of 4 points.
I hope this isn't too confusing. It is one of those things where I know what I mean by all of it, but it isn't that easy to communicate. My goals here are twofold:
- Higher level fighters should be rightly feared. When a party goes into a brawl with a creature with 6 HD and a d4/d4/2d6 attack routine they are rightly fearful. So, too, should someone be when facing a 6th level fighter.
- I want players of fighter types to have some tactical options during combat. Even though fighters are my favorite class to play, it can turn to drudgery when a drawn out combat turns into a monotonous succession of nothing but "to hit" and damage rolls. To sit quietly waiting for the DM to shift his attention to you and your "turn" is over in all of three seconds is not very satisfying. It often leaves me feeling a bit powerless and at the mercy of the dice.
Lastly, I want to reiterate that I have no group, so these ideas are untested. I'm not a number-cruncher, I eye-ball these sorts of things and just do what "feels" right to me. As always, I welcome comments and feedback, especially from the mathematically inclined, who may have some insights into how these bonuses feather in with the "to hit" matrices and anticipated damage outputs, in the RAW.