Instance/quest grinding should both be pretty fast. Quest reward experience was boosted prior to WotLK release, so that Outland quests that used to reward ~9000-12000 exp now give you ~20000-25000+ experience. Skip the ones that take too long (collection quests, obviously) and grab as many kill quests and quests that the group completes at once (such as escort quests).

Instance grinding is also good because the exp rate is pretty high compared to grinding on non-elites, plus you're not interrupted (which is of particular concern on a PvP server). I think some people used Blood Furnace to level to 68 since it's a pretty fast and pretty easy instance to run, but I haven't tried it as a level-appropriate group (I've been PLing with my 80 hunter).