I've made a few modifications to Action Point usage over the years myself, and the Trailblazer ruleset makes a few others. A little bit later in this post, after I'm done talking about why I want them, I'll post my complete Action Point houserule; every way in which they can be used.
To me, Action Points represent two things. The first is that if I'm going to play a swashbuckling game with slightly over-the-top (I would say heroic, but most of the PCs I get are rogues and scoundrels, not heroes) characters, then Action Points give them a way to get just a little bit over the top; to give them a boost when they almost, but don't quite make it. It encourages riskier (and therefore, more fun) play rather than conservative, careful play. The second thing that it does is substitute for other things that I'm taking out. In particular, it makes it possible to have a lower magic game without significantly handicapping the player characters, because Action Points can (to a certain extent) compensate for lack of magic.
In any case, here's my complete Action Points houserule:
All player characters (and select non-player characters) get a total of three action points per session. These may be represented with coins or tokens that are handed out and turned in as used, or they may be tracked independently by the player. Regardless of how many are used each session, action points do not carry-over from session to session, and player characters always get three for every session in which they play. Action points can be used in any of the following ways:
- Improve a d20 roll. After rolling the d20 roll, but before the GM announces success or failure, a player may opt to spend an action point to improve the roll. The player then rolls 1d10 and adds the result of that to the existing d20 roll. This applies to any roll that requires a d20, including (but not necessarily limited to) attack rolls, saving throws and skill checks.
- "Healing surge." At any time, even when it is not the player character's turn, a player can spend an action point to get a "healing surge." A healing surge mimics the effects of a potion of cure light wounds, i.e., the character re-gains 1d8+1 hit points immediately up to the character's maximum, and any character that is dying immediately stabilizes as well.
- Confirm a critical hit. A character who has failed to confirm a critical hit by rolling normally can spend an action point to automatically confirm the critical hit.
- An action point can be spent to gain an additional use of a limited use (i.e. per day) character ability.
- An action point can be spent to gain an additional move or standard action in combat.
- Subject to GM approval, an action point can be spent to emulate a class or character ability that the character does not have. This only applies to one use abilities, not continuous abilities. i.e., it could be used to emulate a barbarian rage, but could not be used to emulate darkvision, because Rage is a one-time use ability with a definite (and short!) duration. This is, again, subject to GM approval. Do not expect to emulate the ability to cast 9th level spells, for instance. It won't be approved.