When one is looking at heirlooms for alts, they are looking to make the leveling experience faster both with the increased stats (heirlooms are considered to be equivalent to same-level blue items) and through the experience point bonus. Which heirlooms you pick for your druid depends on which spec you plan to level as.
Regardless though, an heirloom item I haven't seen mentioned yet is Dread Pirate Ring. Not easy to obtain, but still gives an added 5% experience bonus for kills and quests.
With stamina being the main stat on the ring, it would stand to reason that it would suit melee characters more than casters, but as anyone who has leveled a caster knows, casters too get smacked up too, and a bit of stamina doesn't hurt them any. Hit and crit will help everyone as well.