Idea #1 - XP for rescue and assistance
Maybe rescuing someone from the clutches of the bad guys ought to be worth some XP. 100xp per level of the person rescue might be a good starting benchmark. Count low level but important people as higher level for purposes of this calculation. (E.g. the richest merchant in the land might be a 1,000 point rescue, even though he's a 9 level chump.) Whether this XP is in addition to or in lieu of XP for reward money is up to the stinginess of the DM. If the PCs mistreat or further endanger the poor wretches, XP ought to be reduced.
"Assistance" is worth half as much as rescue, and could be interpreted broadly. Help a treant find the missing piece to the 5,000 piece puzzle he's spent 150 years trying to complete would be worth treant HD x50.
Idea #2 - XP multipliers by AlignmentLawfuls - Double XP for rescue and assistance, double XP for chaotics defeated (suddenly, a reason to be lawful!), half XP for lawfuls defeated
Neutrals - Double XP for treasure, double XP for any monster defeated by non-combat means
Chaotics - Double XP for Lawfuls defeated, double XP for any treasure not split with other party members
Obviously all this doubling is going to speed up advancement. More importantly, by giving characters different goals it forces the party to negotiate over why the heck they are even in the dungeon.