It looks like they're all 30 seconds...either through skills or equipment, are there any abilities that reduce this cooldown?
There is nothing you can do to alter this cooldown. The cooldown was implemented in the game in order to avoid people spam healing. Minimizing the cooldown would basically be eliminating Blizzards intent by implementing it in the first place. There is much more skill and tactical thinking involved when you can't just keep healing to full whenever you want too. The health globes have been placed into the game to supplement the rather lengthy potion cooldown.