I have a modified form of Wound Points made up (haven't playtested it at all yet). All it does is it tries to fix the entire "You're either conscious and able to act with no penalties, or you're unconscious and dying" problem some people have with hit points. This will keep characters alive a bit longer, and hopefully doesn't require any retooling of the various cure spells.
The biggest detriment to the system is that it will take longer for characters to gain any benefit from the Great Cleave feat. Since monsters have Wound Points added to their hit points, one-hit take-downs on low hit-dice creatures are much harder to achieve. (This is why I haven't implemented it in my campaign yet)
Here is the system, simply cut, pasted, and modified from the SRD.
Hit Points, Wound Points, Disability, Dying, and Death
In addition to a character or creature’s normal hit points, they have a number of Wound points equal to their Constitution score and modified by their size. All damage done to a character or creature is taken from their hit points first. When a character is taken to 0 hit points, he is disabled and all additional damage is taken from the character’s wound point total. Wound points can only be taken off if the character has 0 hit points, and are always healed first. Characters or creatures with a Constitution score always have at least 1 Wound Point.
Wound Point Modifiers for Size:
Fine: x1/16
Diminutive: x1/8
Tiny: x1/4
Small: x1/2
Medium: Standard
Large: x2
Huge: x4
Gargantuan: x8
Colossal: x16
Disabled
When a character's current hit points drop to 0 and he has taken at least 1 point of wound damage, the character is disabled. The character is not unconscious, but is close to it. The character can only take a partial action each round, and if the character performs any strenuous activity, the character takes 1d4 wound points of damage after the completing the act. Strenuous activities include running, attacking, or using any ability that requires physical exertion or mental concentration.
Dying
When a character's current wound points drop to between -1 and -9 inclusive, the character is dying. The character immediately falls unconscious and can take no actions.
At the end of the character’s turn each round (starting with the round in which the character dropped below 0), roll d% to see whether the character stabilizes. The character has a 10% chance to become stable. If the character doesn't, the character loses 1 hit point.
If the character's wound points drop to -10 (or lower), the character is dead.
A character can keep a dying character from losing any more wound points and make the dying character stable with a successful Heal check (DC 15).
If any sort of healing cures the dying character of even 1 point of damage, the dying character stops losing wound points and becomes stable.
Healing that raises the dying character's wound points to 0 makes the character conscious and disabled. Healing that raises the character's hit points to 1 or more makes the character fully functional again, just as if the character had never taken any wound points of damage.
Death
When a character's current wound points drop to –10 or lower, or if the character takes massive damage and fails the saving throw (see above), the character is dead. A character can also die from taking ability damage or suffering an ability drain that reduces Constitution to 0, or if the character takes enough Ability Wounds to exceed his current Constitution score.
Healing
Natural Healing: A character heals 1 wound point plus his Constitution bonus per day. Only when the character has fully healed all of his Wound Points can he begin to regain hit points normally.
Magical Healing: Magical Healing always heals the character’s wound points first.