I already started a thread about this on the Races & Classes board but i think this would have probably been a better place for it.
A common complaint i have heard is about the swinginess of rolling hit points. For example, it is easily possible to have two identicle 10th level fighters with a difference of over 20 hit points because of this.
I recently had a friend who felt really gibbed when his character (the party meatshield) rolled 17 on 5d10 for Hitpoints (this did increase to over 30 though after adding Con and stuff) and the GM didn't allow him to re-roll his hit points. The big problem with the current system is often players can be left feeling highly disadvantaged with their character just because a handful of dice rolls didn't go as well for them as the other players.
A couple of possible fixes we have come up with are;
1. Whenever hit points are rolled the minimum value you can get is half the total value (ie 3 on a d6, 4 on a d8, 5 on a d10, etc.)
2. Reducing the dice rolled and giving them a set bonus per level (ie 1d4+2, 1d6+2, 1d8+2, etc.)
3. Giving each class a class bonus plus 1d4 hit points per level (ie 1d4+2, 1d4+4, 1d4+6, etc.)
The average hit points/minimum hit points per level for each of these would be;
MINIMUM HALF:
1d6 - Average: 3.5, Minimum: 3 (Per Level)
1d8 - Average: 4.5, Minimum: 4 (Per Level)
1d10 - Average: 5.5, Minimum: 5 (Per Level)
SET BONUS:
1d4+2 - Average: 4.5, Minimum: 3 (Per Level)
1d6+2 - Average: 5.5, Minimum: 3 (Per Level)
1d8+2 - Average: 6.5, Minimum: 3 (Per Level)
CLASS BONUS:
1d4+2 - Average: 4.5, Minimum: 3 (Per Level)
1d4+4 - Average: 6.5, Minimum: 5 (Per Level)
1d4+6 - Average: 8.5, Minimum: 7 (Per Level)
TRADITIONAL (for comparison):
1d6 - Average: 3.5, Minimum: 1 (Per Level)
1d8 - Average: 4.5, Minimum: 1 (Per Level)
1d10 - Average: 5.5, Minimum: 1 (Per Level)
Of these the Set Bonus option is probably my least favorite. It pushes up the average hit points per level but still gives larger hit dice characters a chance of being screwed with it's low minimum hit points.
I do like the Class Bonus system but using it will lead to much higher hit point characters on average with the average hit points and minimum hit points getting much larger as the hit dice increase.
I think that the Minimum Half system is my favorite as it feels the most elegant and keeps the averages the same as they were.
I would love to hear some more thoughts on this.