Interaction between players

I think one fault of traditional "D&D" is that it fails to encourage a lot of interaction between players. The only choices you really have are (A) support the party or (B) don't support the party. You can either be tactically effective, or ineffective. Alignment is typically a straightjacket, where wildly different alignments are mechanically bad (1e's morale rules, 3.5's spells that keyed off of alignment, etc) or meaningless. You can either freely share your character resources (a cleric passing out heals, for example) or... well, you don't. See how long that lasts. Splitting up loot is usually the most conflict a group will have but that's easily settled because most of the loot is easy to distribute -- the mage wants the scrolls, not the magic plate mail. Also, handing out loot has a lot of bookkeeping, which doesn't appeal to many players, so they just don't get involved and one or two folks dominate the process.

Thus, players don't really have a whole lot of reasons to interact with each other. Usually they're clamoring for time with the GM. This is why even EGG's campaign moved to getting a co-DM -- when the game is so heavily focused on interaction with that one role, you need a good player:GM ratio to allow enough interaction to keep folks engaged.

What if players had an incentive to interact more with each other? Think of a Diplomacy or Settlers of Cataan game, where player-interaction is the main mechanic. No GM is needed but you often get rich, interactive gaming experiences. Even MMORPG's have this interaction beyond tactical support to some degree with crafting, the economy, etc.

Players need some sort of valuable resource that they can trade, but it can't be so essential to character survival that generating conflict over it (because let's face it, competetition and conflict make things interesting) becomes a death-wish and thus socially unacceptable. A few ideas, just brainstorming:
- Raw materials harvested from monsters (usable for multiple things)
- Processed goods (made from multiple raw materials, used for multiple types of characters)
- Oaths or promises
- FATE points or the like

The trick is to make it rules light-enough that you avoid the treasure-trap of obnoxious bookkeeping.

Any other ideas?