Where's the best area to level in WoW for lvls 37-40?

I'm a night elf druid, level 36, and my fiance wants to help me level (56 pally) so we can play together in higher areas. Where would be a good place for him to take me where the mobs aren't any higher then probably 45ish (to be safe-ish for my druid). Any recommendations would be great.